If you like Half-Life 2...
... you might just get some decent times from Timeshift.
I played the first hour of this back in 2008 and didn't care much for it. I pulled it out of my collection recently and started again... got past the first hour (still pretty awful) and then began to really enjoy it. The time slowing/stopping/reversing are really a whole bunch of fun to use, and keeps the combat interesting. There are few puzzles scattered through the game which require the time powers, but they are very simple and not really worth the price of entry. Really enjoyed the environments as the game progressed. and there was more than a hint of the atmosphere of Half Life 2 at times during this game. The graphics are more than serviceable for a 3 year old game.
If you are after a shooter with something a bit different give this a go. You may be surprised at how much you enjoy it.