TimeShift is a shooter with a very cool gimmick - the ability to manipulate time. Unfortunately the game itself doesn't really capitalize on the time manipulation mechanic because if you remove this aspect of the game you'll find that you're left with a very rudimentary, by-the-numbers shooter.
Trying to figure out the story behind the game is even harder than wrapping your mind around relativity's twin paradox. As near as I can figure it, someone has stolen a time-travel suit and used it to apparently become some sort of future world dictator. You, whoever you may be, have taken the only other available suit and have teamed up with an apparent rebel movement. They all seem to know who you are and feel comfortable giving you orders although you're never quite sure who you're supposed to be. There's also a computer voice that gives you hints and information, but it's not clear if it's coming from the suit, the past, or from some ill-advised experimentation during a trip to the 1960s. My advice to you is to not worry about the story and just concentrate on running around and killing everyone who turns your aiming reticule red.
The really cool thing about your mysterious suit as far as the gameplay is concerned is that it allows you to freeze, slow, or reverse time itself. You can pause time and walk up to an enemy and take the gun right out of his hands. You can slow it down and run rampant among an entire squad of enemies. You can reverse time and send the sticky grenade stuck on your back right back into the hands of its thrower. Time manipulation also helps you to master your environment. Need to cross a pool of water electrified by a downed power line? Freeze time and safely walk across the surface. Bridge destroyed before you were able to get across? Reverse time and dash across before it is destroyed. As you can see, such power is rife with possibilities for some really interesting battles and puzzles. Unfortunately the game does not realize its potential and while it can be fun you're left feeling that it could have been so much more.
The first problem is in the level design. The game is unflinchingly linear, keeping you on a tight and controlled path through each level - you ride the dreaded rail, so to speak. Each obstacle that you face is so simple and straight-forward that you'll be left with the constant wish that the game would challenge you more. You're constantly doing rudimentary things with your powers like pausing time to walk through flames or to pass through a gate before it slams shut. Each time you reach an obstacle you'll instantly know what you need to do without giving it much thought at all.