this game is one of those that just flies under the radar. its really cool and worth multiple playthroughs.
there are three time powers you can use:
reverse time: you wont use this much besides a couple of plot puzzles. the only real use for it in combat is when you get hit with a sticky grenade. it'll send it back and give you a brief window to avoid getting hit again.
stop time: this one is also used in a number of puzzles but its actually useful in combat. you can stop time and get easy headshots or you could use it to stop enemy fire and recover your health. of course because its so overpowered it doesnt last very long.
slow time: this one is by far the best. it lasts the longest too. you move at normal speed but everyone else is really slow. its a lot of fun running around getting headshots on everyone.
overall a great game. i definitely recommend it. of course with all the other games available you should probably wait for one of the big seasonal sales to buy it.