One of the Best Arcade games on the Xbox Live Marketplace.
The Game does feature Online Multiplayer, Co-Op, and a Leaderboards. Its also only 400 points on the Xbox Live Marketplace so it is a very good buy.
The levels are called waves. Once you get passed wave 5 its starts to get difficult and it might take a while to get pass wave 10 (depends if you good at this sort of game).
If you like any kind of arcade games and like a challenge you'll love this game.