I tried Assassins Creed, but it didn't really catch my fancy, and was pretty unstable. I wanted to play BioShock since it seemed like an OK way to kill time, but that was pretty unstable too - I'd usually only get around 30min playtime before a crash, so I gave up.
Crysis was a nice game - gameplay was pretty trivial and the storyline was pretty standard, but it sure it darn pretty. It only crashed on me once, and that was when my graphics card overheated after 6 hours of continuous playing
HL2 EP2 was a really nice play, and I'm looking much forward to EP3. The game continues to look great even if the engine is no longer state-of-the-art, and I like the gameplay mechanics and storyline. Portal was a great play as well, had a great time completing that. The bonus levels are a bit too insane, though.
From what I've seen of GTA4 screenshots for PC, I don't think I'm going to bother. It doesn't look all that great (imho only minor improvements from GTA3), but from what people say it requires an insane machine configuration in order to run smoothly even at medium detail quality.
Far Cry 2 has been pretty fun, and looks great even though it's not quite up to Crysis' standard. I like that it's somewhat more realistic than Crysis, though. But it's somewhat unstable, and when it crashes the last couple of savegames are usually corrupted. It's one of the few games that seems to utilize all four cores of my quadcore pretty well, but I can't help but think how well
it utilizes them - after all, the game seems simpler than Crysis, but sucks up more CPU power. The gameplay is very repetitive too, but it's fun for a couple of hours now and then, driving around and sniping people
I revisited DOOM a couple of months ago, completing all four episodes (what, you thought there were only three? Didn't know that ID software released "Thy Flesh Consumed"?) on Ultra Violence. Ah, the nostalgia... and still a great game.
The best game I've played this year has to be Left 4 Dead
. It uses the source engine, so it runs really great, and it looks very nice as well. And I love zombie movies. The gameplay is very nice, both in cooperative and versus modes... this was the game that finally made me buy a head-set in order to coordinate stuff properly with my buddies.