GTA in my opinion is one of those games you should skip a generation, then play the next generation. The formula does get stale but if you haven't played in a long while, or have never played a GTA it's really addicting. I skipped 4 because I played the heck out of San Andreas. I'll probably be picking this one up.
This. I've dabbled in multiplayer on PC with GTA 4 but never played anymore than... 3 hours combined. I haven't seriously sat down and played a GTA since Vice City and San Andreas.