Don't get me wrong, the arcade maps in Timesplitters are great already, but I'd like to see some of them remade for the next-generation. Perhaps they could build on the Chasm level, I felt that it wasn't all it could've been...planet X for the first game wasn't pretty to look at either. They can keep the tunes that were made for them, the theme used in scrapyard from TS2 has something to it that just makes you want to burst Elvis' head open with miniguns. I disliked how there were too many Soldiers in the second game, they practically made up a sixth of the roster; but I wouldn't mind if they only brought back the Siberian or Special forces...I didn't use the others which were just color swaps.
Another idea I have is that all or most characters should have "character abilities" which mean more than just how fast or fire-proof they are. What I mean by the latter is that depending which character you pick determines their skill (i.e. Timesplitters would have cloaking abilities or shoot homing lightning). I also suggest that the temporal uplink should be available for use in Arcade mode, It'd be interesting to kill someone via flying watermelons. There should also be more weapons and bots available on the maps, it would certainly add to the chaos of the multiplayer experience...not only would you have to dodge bullets, but now flying monkey heads and whatever else you can pull off the ground.
Please make a Big Daddy parody as a character...