I've just been going on about how great Mars: War Logs is. It's on the 360 for $10. Try the demo first though.
Mars: War Logs, like all the Spiders games I've played, is a fairly good game that could have been really special but didn't come close to living up to its potential. It has some good ideas, but it falls into a really tedious pattern of repetition and has some of the most atrocious dialogue and voice acting you will find anywhere this side of a Reality Pump game. Still, it's thoroughly worthwhile, especially considering the meager asking price.
Dialogue and voice acting was completely redone by Kalypso some months after the game was out.