Been there, done that. The formula hasn't changed, but there are a few notable changes.. some good, some... not so good.
But then again, a few things are taken out. You can't pilot airplanes. Helicopters are still in the game though. Can't parachute either (as far as I know). You can't pimp out your rides either which was a great plus in San Andreas.
I'm going to keep this short. This game is great, definitely work the money if you are a GTA fan, but don't go into it expecting a perfect 10 game. This game isn't. It's great, masterfully done, but it lacks some of the fun factor that the other GTA games (the more recent ones) had. Maybe this game deserves more than a 8.5. I'm guessing it should be sandwiched somewhere between 8.5 and 9.0, but definitely not the 10s its getting all over the place.
Great game. Doesn't live up to the hype though.