Unique Ability: Treasures of Nineveh
Every time you capture a city, you gain a free technology that the city's owner has, and you do not. If you're completely ahead in tech, this does nothing.
Unique Unit: Siege Tower
Replacing the catapult, Siege Towers grant a bonus to attack against cities to all adjacent melee units. The tower itself can only attack cities.
Unique Building: Royal Library
Replaces the regular Library, and grants +1 Science for every citizen in the city where it's built. It also contains a slot for a Great Writing (part of the new Culture system) which, when filled, grants all units trained in the city with an xp boost.
Adviser T.J. says:
Assyria was always my biggest rival in the few games I played in the press build. Their civ ability makes it possible to spend most, if not all, of your resources on military early on, and steal your way back up the tech tree as you conquer. Taking cities is always tough in the early game, but Assyria is great at it. Once you get a Royal Library, your science scales based on population—so I would recommend taking Tradition policies, keeping your empire small and well-fed, and razing most of those cities you captured for the tech boost.