The Huns are purely an offensive civilization. Like the Goths they are great at rushing, thought the Huns focus on cavalry instead of infantry.
Since they don't need to build houses they are great at rushing since the resources and time spent on houses can be diverted to building an army. Their unique unit, the Tarkan, is fast and relatively tough cavalry unit that is great at destroying buildings and archers, making them effective raiders. They have effective cavalry since in addition to Tarkans they can build Paladins for heavy duty combat and Cavalry Archers for quick ranged support. Cavalry Archers are cheaper than normal for the Huns so will likely make up a large part of a Hunnic army. Their trebuchets are more accurate than those of other civilizations which aids them in destroying enemy buildings or siege weapons from a distance. The Huns' faster stables allow them to replace lost Paladins faster.
The Huns are one of the most powerful civilization in Deathmatch games, because as they don't need houses, all three of their starting villagers can be tasked with building military buildings.
Their infantry are weaker as they lack the Champion upgrade. In addition their siege weapons are somewhat lacking, missing the Onager and Heavy Scorpion upgrades. They are geared purely for offense. They have a pitiful defense that can be easily broken. As such players should not spend resources on building defensive structures. Instead they should spend them on more units to constantly attack the enemy so they won't have the chance to attack in the first place.
While the Huns remain viable in the late game, they are generally very predictable as their only strong Imperial Age units are Paladins, Trebuchets and Heavy Cavalry Archers. This lack of flexibility in their army composition can easily put them at a disadvantage.