It's GTA, but with an innovative twist!
There isn't much of a story to the game. There are gangs; You must destroy them. While doing so, you can collect upgrades and level up your agent so he can be stronger, faster, and more skilled at everything he does. You can also upgrade the Agency cars you drive so your driving skills can increase.
I'm worried that one of the reasons people will buy this game is merely for the Halo 2 Beta. While that is a big plus, you may soon find yourself sucked into the game. Although, once you get tired of the single player mode, you can hop online with Crackdown's Co-Op mode. This is where it's at. You can bring your agent from the campaign and upgrade him while playing in a friend's game, helping him or her get further in the single player mode. You can make your friends jealous with all the sweet upgrades you have, that they don't. Once you've left their game, you'll also have everything you've picked up or earned while you were there, like new weapons.
Overall, this is a pretty decent game with a GTA touch but more innovative ideas behind it. The graphics aren't meant to be spectacular, but they work well for the game. The sound is decent. The game does lag up at times, but that's nothing to get worried about. If this review doesn't help you make a decision, go and rent it. You'll find yourself pulled into the game in no time.