Fallout: New Vegas.
I played Fallout 3 when it came out, but I didn't really enjoy the game that much. There were just alot of niggling annoyances that kept bugging me, not the least of which being the massive bugs (I was playing the PS3 version, which I've heard was the worst offender in this regard).
So I wasn't exactly overjoyed then New Vegas came out. But I heard that some of my issues had been addressed, so I decided to play it... eventually. Picked it up from my local Blockbuster used for 15 bucks.
Do not regret the purchase at all. I just finished it yesterday, and I enjoyed it SOOOO much more than FO3.