I don't really have a favorite game. I have games and series that I have a high loyalty to, though. I love the Dynasty Warrior and Resistance series. I loved Batman: Arkham Asylum, and was stoked to hear AA2 was officially announced. I also am eagerly awaiting Assassin's Creed 3, as well as the recently announced new AC game that will also have Ezio in it. I enjoyed the Saint's Row series (despite all the bugs) and have every GTA game (except for the one for the DS). I'm really looking forward to Fable 3, though it sounds like it's going to use Natal, which I don't especially care about at this point.
My loyalty to Halo wavered after 3 (I just can't bring myself to pay new-game prices for ODST when it is really just an expansion, and as a result, am hesitant about Reach), and CoD after 4 (at this point, I think they're just throwing the same stuff out with small tweaks here and there).
Anybody who feels like adding me, my XBL is notagoodtageleft (Be warned, though, I don't have a gold subscription any more). My PSN is NotU. I don't remember my Wii code off the top of my head, but if anybody wants it, just send me a pm and I'll look it up.