I'm sure you're looking for something similar, but sadly, there aren't many games out there quite like TimeSplitters: Future Perfect.
I'll throw a recommendation out there that isn't as well known, but still awesome. Monday Night Combat is on both XBLA and Steam for $15. It's the combination of a team-based/class-based shooter and a tower defense game and it's a blast. I was also gonna say Battlefield: Bad Company 2 (or just wait for Battlefield 3, which looks great) but neither seems to be the kind of game you guys would go for I assume.
*Explodes*
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Moo
"I can't see there's an oliphaunt in the way" - foolmo