Timeshift, a first person shooter who's quality is very variable, with some great parts then parts that are boring, but the good parts of the game can be very good. It's a first person shooter, where you can control time, so that you can pause the game world, put the world into slow motion, and even reverse time, though not for more than a few second, and then you have to wait for your time control mechanism to recharge (which takes about twice as long as the pause/slow motion/rewind function lasts).
The problems with the game are that it feels linear (most FPSs are linear, but the good ones tend to fool you into not noticing it), the quality of the levels varies greatly, the story is very badly told (I've completed the game several times, and still can't remember much of the story), it has recharging health/shield, a weapon carrying limit (though at least it's three weapons in this game, not two), and the game's ending makes you want a sequel, which never came since this game sold so badly.
On the plus side, the game is often a lot of fun, the weapons are great, the alternative timeline is pretty atmospheric, and the time powers are a lot of fun to use. Plus, if you like weather effects (I do), the rain is great in this game, very realistic, and looks fantastic when you pause, slow or reverse time.
If you like first person shooters, then you should give Timeshift a go, especially as it's bound to be really inexpensive now, used.
Operation Flashpoint, a military first person shooter that aims for realism, and not in the way that modern military FPSs aim for realism. In this one you are very mortal, and you can say spend twenty minutes sneaking up to a set of buildings that you believe are inhabited by the enemy, then when you poke your head out of a bush, you get headshotted and die due to a sniper you hadn't noticed. You get to pilot and drive lots of vehicles, and the game is so realistic that even the speed of sound is simulated, so that if you see say a very large explosion in the distance, then you won't hear it until the sound has reached you (because sound travels much slower than light, of course). It's not a linear game, it's much more open ended and open world, and you can interact and interfere with both your own side and the enemies. I don't like this game at all, and I've never gotten far in it, since it's too realistic to be fun, but it was massively popular with some gamers. They made some sequels, but I don't know anything about them, I only played the original.
