Crackdown for the Xbox 360 is a sandbox style game, kind of like Grand Theft Auto only with less of a story-line. The game doesn't really have a storyline and simply consists of running from boss area to boss area wiping out bad guys and killing the leader. Even with the simple design this is quite a fun game and gives the player plenty to do.
The variety of weapons available in the game isn't too great but there are quite a few vehicles which are pretty cool to drive.
The best part of Crackdown is in the ability to play online with other people; the game is a lot more fun running around the city with a partner. I've had a lot of fun playing with friends online but still wish the game supported some kind of local multiplayer.
Overall Crackdown is a game that I would recommend gamers rent before they buy; the experience wears out fairly quickly and the game isn't for everyone.