I have a couple. One, Oblivion on the PC. The modding community and the console made it a game with unlimited roleplaying options. Two, Fallout: New Vegas. Fallout 3 was probably better but the revamped Repair skill was awesome. I can't help but feel awesome and self-sufficient when I run across a wasteland, taping, gluing and jury-rigging my guns. Three, GTA IV. The PC version was epic. The trainer plus Independence FM. Last one, Fable 2. Yeah, I know what you're going to say but I really couldn't stop finding stuff to do in that game. Max out your 1337 sk1llz, commit bigamy, open doors, shag with 20 people at the same time, plus, A nice, simple combat system that was way to easy, but still fun and satisfying. I also like Mercenaries 2, mostly because you can just say 'screw you, objectives!' and ride around Venezuela in a jeep with your PLAV homies. Not to mention Deus Ex Human Revolution. Brilliant, but strangely reminds me of Half-Life 2. The list goes on: Just Cause 2, Fallout 3, MGS Peace Walker, Assassin's Creed Brotherhood...
Worst value was probably... Operation Flashpoint: Dragon Rising. It had a good concept but it was way too hyped. The cinematic trailer (the one with silenced SMGs and the helicopters landing and rapid fire and stuff) made it look like a fast-paced, intense military simulator where you needed to take advantage of every asset and think quickly to survive and win. The end product was a sluggish, heavy handed FPS with a high bullet damage matrix. Also, Gran Turismo 5. Ugh.