Just read through all of them, some very good responses. Clearly a lot of people aren't into reading about video games on the internet.
I agree with Thorp for the series (at least I currently do, it might change when I place my vote). GTA has been huge for videogaming, bringing it attention it didn't get through controversy, selling millions of copies, and spawning many a wannabe. The detail on the cities is incredible, the storylines, characters and voice acting superb.
Also, their experimenting with DLC really gets me excited. You're not downloading new armour or a couple extra levels; you're downloading a whole new experience.