The Goths are an offensive civilization with the ability to rapidly produce infantry at reduced price in the late game. They have somewhat respectable archers, cavalry, siege and navy as well, despite their absolutely terrible defense.
They are great at rushing since their infantry units are cheaper and created faster than those of other civilizations. In addition, their Pikemen or Halberdiers are also cheap and very useful against enemy mounted units, Huskarls are useful against enemy archers, and both Huskarls and Champions are good for destroying buildings due to the attack bonus. Also, they get additional population space in the Imperial Age.
Their unique unit, the Huskarl, is an infantry unit that is almost immune to archer fire. They are powerful units and usually form the core of a Gothic army. The Goths already have a 20% bonus in Barracks production speed and they get another 100% boost with Perfusion (although in The Conquerors it states it's 50%, it's actually 100%), one of their unique technologies. Their other unique technology, Anarchy, allows Barracks to create Huskarls. This allows the Goths to rapidly produce an army of infantry and can overwhelm an opponent with sheer numbers. The fact that they are able to produce an infantry army much faster than others also means opponents are often unprepared to fight off a massive attack. If an attack fails, they can rebound very quickly (especially with the help of Conscription and Perfusion) and have a massive army again before the opponent can recover, assuming they have enough resources. Because of their ability to rapidly train a large amount of soldiers the Goths are quite powerful on Deathmatches, where the large amount of resources gives them a distinct offensive edge. Finally, the Goths also have decent units and upgrades of other categories as well, such as Hand Cannoneers, cavalry with Bloodlines, Bombard Cannons (though without Siege Engineers), and Shipwright, meaning they have a well-rounded offensive capability.
The Goths have some large drawbacks. They have the weakest defense of any civilization in the game as they cannot build stone walls or upgrade their towers beyond Watch Towers. They can only rely on Palisade Walls and Watch Towers for defense. As such, Gothic players must constantly be on the offensive since they won't last long if forced to go on the defensive. While the Goths have strong anti-archer capabilities, their own archers are somewhat lacking. They cannot research Thumb Ring or Parthian Tactics and lack the Arbalester upgrade. However, the Goths are given Hand Cannoneers as an anti-infantry ranged support should the enemy try to counter their Huskarls with Champions. Their siege line is also lackluster, lacking the Siege Onager and Siege Ram upgrades in addition to lacking Siege Engineers. However, the Goths do have Bombard Cannons as a compensation to clear out enemy siege weapons and buildings. Additionally, Goths have severe issues with fighting units with anti-infantry bonuses and very strong melee armor. Cataphracts, Jaguar Warriors, Teutonic Knights, Samurai and Boyars are devastating to the Goths' infantry armies (though by mixing cheap Halberdiers and Champions with Hand Cannoneers, they can hold their own).
Goths have only one effective strategy, but it is among the most feared and dangerous in the game. Their Dark Age is fairly normal; so the player must age up on 22 population (21 Villagers) for a Feudal Rush (flush). The flush itself is a relatively standard infantry flush, although they can field far more troops for a comparable price, and they have an attack bonus against Buildings. The idea is to keep the foe off balance so they can't build up, since Goths are severely lacking in any form of conventional defense.
Upon reaching the Castle Age, Goths must upgrade their Men-at-Arms to Long Swordsmen, get any relevant Blacksmith technologies, and start mixing in Huskarls. Upon reaching ten to twenty Huskarls, a direct assault on a Town Center is possible, unless the foe has large reserves of melee troops. A good Goth player must use their Militia line for dealing with infantry, the Spear line for dealing with cavalry, and Huskarls for dealing with archers and defensive structures.
Goths have a reasonably good navy, only missing Dry Dock and Elite Cannon Galleons. However, they should generally keep their feet dry unless there is a good reason to take over the water, since their resources are far better spent on troops.
Goths lack Stone Walls and almost all fortifications; however, they can still defend themselves with units and other buildings. A Goth player must use Barracks and Houses as walls, and in case of a rush, troops can be created at an incredibly rapid pace. The Goths though have access to Masonry and Architecture, providing at least some defense for them, especially for their Barracks. As long as they have the resources, simple infantry floods can be a surprisingly effective defense. It's often better trying to defeat a Goth player before they hit Imperial Age and are able to flood with infantry.
Most of the Goths' lategame power comes in the Imperial Age, where they are able to spam a large number of infantry units thanks to their team bonus and Perfusion and completely overwhelm the enemy. The Goths' lategame Huskarls are easily counterable with fully upgraded Champions in terms of cost efficiency since Huskarls will lose 1v1 against a fully upgraded Champion, and the Goths lack Plate Mail Armor. However, if the Goth player uses Champions, even though they lose 1v1 against other Champions, their cheaper price and faster production rate will make them win in the long run and, in terms of gold efficiency.
Goths along with all other civilizations receives the new Arson technology that gives infantry units attack bonus vs Buildings, and this also furthers up the infantry's attack bonus against buildings making them even more effective.
The Goths are the only civilization not to get the Supplies technology. This is meant to balance out their already cheap infantry and their ability to mass produce their infantry. That being said, other civilizations having the Supplies technology means other civilizations can approximate the Goths' mass production of Champions in the late-game, especially civilizations with already strong infantry bonuses and unique technologies, such as the Japanese, Aztecs, and Slavs.
With update 35584, they are now able to perform a very potent Militia Dark Age rush, as their discount bonus now applies since the Dark Age. Update 36202 significantly nerfs the Goths by having their discount bonus scale in age and lose the Arson technology, but their civilization bonus boosting infantry attack against buildings now scale in age starting in the Feudal Age. They also receive free Loom in Update 36906, allowing the Goths to produce more Villagers in the Dark Age and save more gold for their Militia Dark Age rush.
However, in update 42848, Goths lost free Loom, but they can now research Loom instantly, because the Goths motivated the "laming play" (stealing enemy Boars) thanks to the extra protection for Villagers. It also allowed them to make up to 6 Militia for rushing in the Dark Age without mining gold, which was widely considered unfair. The Goths can still get one extra Villager before advancing to the Feudal Age.
In team games, the ideal mates for the Goths are the Aztecs, Slavs, Italians, Malay, Burmese or Vietnamese. However their team bonus is highly valuable for infantry based civilizations such as the Malians as it aids spamming infantry.
Aztecs: The Aztecs benefit from the Gothic team bonus and will produce their barracks units 35% faster in total. The Aztec team bonus of more relic gold can help the Goths keep up a steady stream of infantry in the mid and late game, as long as the player takes the additional care of collecting the relics.
Berbers: Allying with Berbers allows the Goths to receive Genitours to screen their infantry from enemy archers, for not all Gothic infantry are as resilient as Huskarls, plus Kasbah to spam Huskarls and Trebuchets even quicker. In return, Berber Champions can also be spawned rapidly to support Genitours and Camel Archers.
Sicilians: It may not be an ovbious choice for an alliance, but considering the creation speed for the Goths' infantry and their extra 10 population in the Imperial Age, this means that the Sicilian technology Scutage can pay substantial amounts of gold to the Goths.
Slavs: As an infantry civilization, the Slavs also benefit from the faster barracks. Their 5 population for military buildings can help with the Gothic infantry rush and save some wood.
Italians: The Italian Condottiero is a great counter to gunpowder units such as the Hand Cannoneer, which can be very dangerous for Gothic Huskarls and other infantry.
Malay: A Malay ally grants Gothic Docks line-of-sight boost that allow them to build solid coastal defence and fast-response garrison fleets to counter naval invasions effectively, in exchange for abilities to swarm their opponents to death with their mass-producible infantry hordes, particularly after Forced Levy has been researched.
Burmese: They also reveal and share the exact locations of relics at the beginning, making any of them not too far from the Gothic bases will also be theirs for the taking. In return, the Burmese can spam waves of attack-enhanced infantry hordes in a few minutes.
Vietnamese: They have various tricks to boost anti-archer prowess of their Gothic teammates: at the beginning they reveal the exact locations of enemy Town Centers for Gothic teammates to perform militia rushes, at later stages they introduce Imperial Skirmishers to ward off enemy archers and halberdiers, plus Paper Money as bankroll for their Gothic teammates to amass more Huskarls quickly. In return they also can amass infantry even quicker to protect their missile contingents.
Cumans: Their team perks will be the saving graces for Goth players; their team bonus slightly improves Gothic defenses (+33% more hit points for Palisade Walls). This is especially important as Goths lack Stone Walls. Cumans also grant 10 free Elite Kipchaks to their allies (available after Cuman Mercenaries has been researched) to supplement the infantry-oriented Gothic unit roster.
The Huskarl, being an infantry with high pierce armor, able to be created at barracks (with fast working rate), and attack bonuses against Archers, buildings, and Eagle warriors, can effectively destroy enemy towns, so civilizations with poor defenses (such as Huns, Berbers, Cumans, and Magyars) and civilizations reliant on Archers (like Britons, Vietnamese, and Mayans) may have trouble against them. Even civilizations with good defense (like Byzantines) may struggle against hordes of Gothic Huskarls. They can also counter Scorpions, and to some degree Cavalry Archers, so civilizations like Khmer, Mongols, Tatars and Cumans may also have problems against Huskarls.
As their Halberdiers are cheaper and are created extremely fast (after Perfusion is researched), they are better suited to counter cavalry, as they can outnumber cavalry contingents, so cavalry based civilizations (like Franks, Magyars, Huns, Lithuanians, Cumans, Tatars and Persians) will also have trouble against Goths. This also gives the Goths an advantage at trash wars, especially against civilizations that don't have fully upgraded Skirmishers (like the Turks) or lack the Champion upgrade (like the Persians, Ethiopians, Malay, Khmer, Mayans, and Huns).
As their Militia line are created faster, have more bonus vs buildings, and are cheaper, while also having a nice early economic bonus, they have an advantage in open maps against civilizations with bad early game (like Turks, Spanish, Portuguese and Khmer), as they can raid since the Dark Age. This also gives the Goths a second advantage at Trash Wars, as the Champion, despite not being a Trash unit, is considered a counter to almost all Trash units.
Since they have access to Gunpowder units, they can effectively counter the infantry of other prominent infantry civilizations (such as Aztecs, Burmese, Slavs, and Japanese), while their bombard Cannons can counter the siege of other civilizations (while also adding more power against buildings).
Since Update 37650, a good number of civilizations have lost access to the Supplies technology, giving the Goths a significant advantage against civilizations that don't have Supplies in the late-game to match their mass infantry production (even civilizations with access to Champions, such as Chinese, Lithuanians, Mongols, and Cumans).
Though the Huskarl is a well rounded infantry against arrow-fire, it lacks melee armor and can be countered by other infantry and cavalry, so civilizations with good infantry (such as Burmese, Teutons, Japanese, Slavs, and Aztecs) can counter a Huskarl horde. The same logic applies for cavalry civilizations when encountering Huskarls (including Franks, Magyars, Berbers, and others). Also, as Onagers deal melee damage, they are a threat to a mass of un-microed Huskarls, so Celts, Koreans, Ethiopians, etc. have ways to counter them. Being infantry means that also Hand Cannoneers and the usual anti-infantry units (like Aztec Jaguar Warriors, Byzantines Cataphracts, Incan Slingers) can counter Huskarls (although keep in note that Hand Cannoneers and Slingers need careful protection, as Goths' Huskarls can gap close on them easily and deal bonus damage against them as well). Japanese Samurai are also a huge threat to Huskarls, Teutonic Knights and Slavic Boyars have enough melee armor and good attack to slaughter them. Shotel Warriors also works well against them due to their high attack. Another good unit would be Viking Berserks, since they can regenerate hit points so they can resist the Huskarl hordes.
Aside from the drawbacks the Huskarls have, as the Goths rely heavily on spamming masses of cheap infantry and not on strength or resilience, other infantry civilizations may be a problem for Goths, especially before the Imperial Age (as in the previous ages, they don't have Perfusion and Hand Cannoneers). Masses of Hand Cannoneers, Aztec Jaguar Warriors, Byzantine Cataphracts, and Incan Slingers are a huge threat to their infantry. Similarly, civilizations with ranged melee units such as the Malian Gbetos, Franks' Throwing Axemen, and Saracens' Mamelukes can pose a huge threat to the Goths' infantry and Huskarls in the late-game.
Civilizations with access to units that deals Trample Damage can also be a problem for the Gothic Horde, especially if they don't mass the corresponding counter to these units (particularly Halberdiers). These may include Byzantines (with their Cataphract), Persians (with the War Elephant) and all the four southeast Asian civilizations, as they can access Battle Elephants. Slavs are a special case, as they can research Druzhina, which enables their infantry to deal trample damage, which also means that Slavic infantry may defeat a larger army than theirs in massive battles.
While being probably one of the best offensive civilizations, their defense is lacking, with only Watch Towers and no Stone Walls, so their towns can be easily destroyed by civilizations with good anti-building units or good siege (such as Ethiopians, Slavs, Celts, Turks and Huns). Civilizations with early game aggression, such as Aztecs, may also be a problem sometimes.
As their hunters carry more meat and they have a bonus vs boars, the Goths have a distinct advantage on maps where they can found more huntable animals than normal, particularly maps where they can find more than 2 Boars (or their equivalent) near their Town center, including Yucatan, Valley, Scandinavia and Black Forest.
As Goths have +10 population cap in the Imperial Age, they can exploit more of this advantage in matches where the population limit is low, with the 25 population capacity being the most ridiculous case (as Goths in that setting in the Imperial Age will get 35 population space). In conclusion, the lower the population cap, the greater the advantage they get from this bonus.
In maps like Arena and Fortress, as there are predeployed Stone Walls, Goths technically overcome one of their weaknesses as they can't create Stone Walls. Also in Fortress all players starts with already has a Barracks so Goths can start spamming infantry from the beginning of the match.
As Goths can rapidly spam their troops, they are surprisingly good at King of the Hill matches in land maps, especially if the player decides to protect the Monument with Barracks.