Americas Army Online is a tactical shooter MMO extremely realistic game.
The game is a very addictive game. More realistic than all shooter games out there. It has real weapons the US forces use. You play as an American soldier, and while there are boot camp missions that serve as both instruction and primer to Army life, they're completely optional. If you want, you can just dive straight into the multiplayer missions. It's worth exploring the boot camp sessions, because you can unlock equipment like special sights and better gear.
The attention to detail is incredible and about as realistic as possible. Your soldiers are armed with all the standard Army weaponry of the day, and are outfitted with the latest uniforms and gear.
There are five maps in the game, most of which are updated versions of existing, popular maps, such as Bridge and Pipeline. Each map also supports multiple game modes.
Compared to other multiplayer shooters, America's Army 3 places more importance on working as a team than on actual killing. Neutralizing a single enemy soldier will get you a single point, but seizing an objective that your squad leader has issued to your fire team will give you four points. You're also punished heavily for friendly fire and for violating the rules of engagement by, say, shooting the enemy wounded to prevent the other side from resuscitating them. The end result is a game that encourages team play.
Overall it is a fantastic game and a good game to get away from those fast action pack games.