Check out this game on the XBL arcade. It's a side scroller space ship shooter. It's simple, but very fun, and best of all its FREE!!! I just spent an hour playing the game online with a couple of guys, I had to eventually stop so I can still have time to go to the gym, otherwise I'll be here all night!

 

Am gonna try it tonight for sure

 

I second the recommendation.

Playing it co-op was insane and the difficulty at time reminded me of R-Type.