Well, I've honestly not had the money to get many of the new games from 2008 (I, sadly, have not yet played MGS 4, but I will get to it eventually!). That being said, here are the favorites of what I've played:
GTA IV
Guitar Hero World Tour
Shin Megami Tensei: Persona 3 FES (borderline on whether this counts, though...the original game came out in 2007, but didn't get much publicity in the US...the special edition, which added a ton of new content, came out in the US in 2008. I'm gonna count it, just because it's one of the best RPGs I've played in years)
I spend way too much time catching up on older (cheaper) games, so my list will probably stay this short for a while.