I really liked TimeShift. It has great graphics and the time controlling mechanics really add to the game play. Multiplayer, with it's Timeshifting grenades is like nothing else out there.
To bad it released around the same time as Bioshock, The Orange Box, Halo 3, and Call of Duty 4. Timeshift, a better than average FPS had no hope against 4 of the best FPS games in history. If you come across Timeshift pick it up, it's a great game and MP is awesome. Send me a friend request on Xbox Live I'll gladly play with you whether or not you need achievements.