I've played through it once, and I like it fine enough. It's not as good as San Andreas or, to be honest, even Chinatown Wars. GTA4 takes away all the zanyness and over the top mission structures I'm so used to seeing. No more fire truck or ambulance missions, and taxi missions are only available for maybe the first quarter of the story. It feels like most of the stuff available to do in this open world is play mini games and go street racing.
See, what they did was take away most of the odd jobs and replace them with one of the most annoying gimmicks I've ever seen in a game--oh, could you hang on a second? I've got a call.
"Hello."
"PHUNKY, HEY! YOU WANNA GO SEE A SHOW!?"
"But we've already seen all the shows in town a dozen times. No thanks."
"WHAT!? I HATE YOOOOOOOUUUUUU!"
*thumbs down symbol appears*
It's the thumbs down part that really makes me hate it. Why the hell should the player be punished for not wanting to play a mini-game? Even worse, you only get an hour to pick the person up, and sometimes they're at the opposite side of the city. I don't think it's even physically possible to drive across the map in one single in-game hour. Maybe if there were absolutely no other cars on the road...and even that's just a maybe.