I played through the main storyline, but honestly it wasn't that fun. The game takes itself way too seriously, Niko Bellic is completely unlikeable, and once you finish the story missions, there's almost nothing to do except shoot pigeons and jump over stuff.
But my biggest complaints are these:
One, the game world is too small, and there's no real open spaces you can really hammer down with a supercar.
Two, while there's *SOME* side missions and stuff to do, but not a lot. Maybe a day's worth of stuff.
Compare that to San Andreas' titanic game world and myriads of stuff to do after the main missions.
The most fun I had in the game was killing Niko. Watching him get launched off bikes and through windshields never loses its charm, especially when he hits something else like a pylon or another moving vehicle. But, you can only do that so much because hospital is really, really, really expensive, and there's very limited ways to make money.