I play Halo as well, but TimeSplitters is just fast and frantic and goofy and great. It's a popcorn game. The story mode is medium sized. But there are a ton of mini games to play, to unlock more and more and more.
Of course, I'm playing this on a PS2. Where there haven't been any good fast paced shooters to play online. Since none of my dang ol' friends own XBoxes.
Hmm mini games? I didn't hear about any of those. I do know it has a map-maker, which is pretty cool. I don't acually own an Xbox anyway, I was just pointing out that Halo is pretty much the only FPS people play anymore.
Ooh! Is there a level editor like there was in Timesplitters 2? I loved Timesplitters 2 primarily because it allowed you to make your own levels (though story-mode options were very lacking for self-made levels).
My favorite level I made had you trapped in a large room with lots of pillars (leaving resulted in losing the mission), and all the bad guys were monkeys armed with various explosives, and all you had were explosives as well. The goal was to survive 3 minutes in a confined space surrounded by bomb-hurling monkeys and having to avoid both their explosives and your own explosives.