Most of mine are from around 5 years ago because that was pretty much the height of gaming obsession. It's quieted down a lot but I still pop in a game every now and then... Anyway, these are my favorites...
Bully - I love the whole idea of the game and free roam environment just makes it that much more amazing. I own the Ultimate Edition which came with an actual dodgeball that you can blow up and play with. Pretty awesome.
Max Payne and Max Payne II: The Fall of Max Payne - Two amazing games that play out like a film noir. I just love it and bask in the environment every time I pop it in.
GTA: Vice City and GTA: San Andreas - Two classics. You can't go wrong. A big piece of my childhood was wasted playing these two.
BioShock - My favorite Ps3 game. Again, I love the environment. The whole 50's style set in a futuristic environment is just so creative and amazing. Nothing like that game.
The Darkness - Love the gameplay and the story. Mob lifestyle boiled in fantasy, shooter water. So great. Can play it for hours, to this day.
Infamous - It's not the best game, but extremely fun nonetheless. Love the idea of being an ordinary guy and then one day just turning into something extraordinary. Like a sick ass superhero. Really fun game,
The Movies - My favorite PC game ever. I was extremely obsessed when I was 14 or 15 and wouldn't leave my desktop. I'm a film major now, so it definitely helped me hone my skills in a way.
Rome: Total War - My second favorite PC game. I have a little obsession with Medieval era Rome and the various rulers. Kind of a history buff, and this game actually taught me to strategize like a Roman general would have had to. Very interesting, fun game.
Red Dead Revolver - Just a really fun game. It's from a sentimental part of my life, and kind of shepherded me toward the Western genre of films (which I'm also in love with). So I think I owe a lot to this game. Spent a lot of time trying to beat it, as I remember. I love the horror aspect of it as well.
Manhunt - Just a sick, sick, sick game that I played at way too young of an age, looking back on it. I just remember being in love with it though. Sick love, but still love.
Condemned: Criminal Origins - This should be pretty high on the list, but I'm just listing them as they come to mind. Very interesting, insightful, scary, fun, immersive game. Horror gaming at it's finest. The Survival Horror genre is probably my favorite.