It's... actually not bad. It has a kind of explodey efficiency to it: high fights-per-second, or something. Nevertheless it's not exactly going to carve itself into the bedrock of our collective memory. It's not looking like a clear classic, but a shooter of medium proficiency. And that's not simply the current embarrassment of riches talking - Timeshift really does seem a few strides short of the podium of greatness. It has a kind of clunkiness of design that's holding it back.
Nevertheless the time stuff works. Yes, Prince Of Persia did rewinding time, and yes various other games did slowing down time. Timeshift is unlike any of them. You can stop time entirely and pull a gun from an unsuspecting soldier's hands. You can slow time and dive through a fight like a lightning bolt. Unlike FEAR you have have to use the time powers, because otherwise the muscular men with guns are going to shred you. Timeshift feels like it's playing to its own agenda, and that's a good thing. Sure, it's a shame the overall game is a little weaker than some of its buffed-up peers, but it's still credible. The shooting is vicious, the physics are PHYSICS! and the big men die in a satisfying manner. Kieron has played a bit more of the full game than me, so he might be able to say more. Then again, he might not. Based on this taster, I'd be interested in reviewing the full thing. I reckon you should downloaded it and judge for yourself.