Favorite single player game:
Prey--for first person shooters, this one is it. If you think you've seen it all, this game will surprise and probably shock you. First, it uses the Doom3 engine, except it's modified. It runs about as smoothly FPS-wise as Doom3 and it is about as demanding on the hardware. You play as a Cherokee indian guy who gets abducted with his girlfiend by aliens, but you, the protagonist has special powers. You can switch from normal mode and spirit mode, which allows you do to special things, like see things that aren't normally there, and get through special passages.
The graphics are simply amazing. Like I said, it's about as demanding of the hardware as Doom3, but the graphics and visuals are quite a bit better. The lighting and the realism of the models are much improved. Your guy uses mainly alien weapons that are biological, so they're wet and slimy looking. And the way the light shines on the weapons as you pass by light sources is--well, you just have to see it. The special effects are amazing, the force fields, the spirit mode, all interact and change the way you see things. Very immersive.
The game play is what really makes the game unique. This is the first game I've played in a long time that has really fucked with me. The enemies are intelligent and pretty challenging, even for normal difficulty. But the game is still a bit too easy. A lot of the game takes place on an alien ship, which the artists did an excellent job on. But this is the first game that has introduced (to my knowledge) a true seemless warp gate. You walk up to a thin panel, and you can see what's on the other side, just by looking at it. Walk behind it--nothing. Just the opposite side. But walk THROUGH it and it takes you to another place. Doesn't stop for a game load or anything. Doesn't even chop up. Very weird and very trippy.
The game also does some VERY weird gravity effects. So if you're not completely confused by the seemless teleporters, you will be fucked up by the gravity switches. There's nothing that fucks with your orientation more than navigating through an area when the gravity keeps getting switched. One moment, you're walking on the floor. The next, you're on the ceiling, the next, you're on the walls. You're trying to get your bearings, while throwing grenades at enemies, and instead of falling, your grenades appear to fall upwards, or sideways, if you happen to be walking on a wall. It is awesome.
You also drive a spacecraft that wraps around you and shoots fireballs and has a tractor beam. Driving it around is a lot of fun and the levels you travel through are beautifully done. The artists did a wonderful job.
I found myself saying, "Holy shit!" a lot when I was playing this game. If you've never played this game and you like FPS games, you cannot miss it. In my opinion, it is about on par, maybe even better than Half-Life 2.
Half-Life 2 is really good too.
For multiplayer, my favorite is Far Cry. Mainly because I am awesome at it.