The only thing I really complained about with GTA was that I felt Rockstar dropped the ball on making sure the online portion of the game was ready to handle the demand on the first week. Everything else about the game I feel is well done. There is a vast map to explore, random side missions, and being able to play with three different characters.
There are some things I wish were included, but they are not necessary, and this is the first GTA game since San Andreas (I enjoyed the PSP games but never really played them to explore the city, and I never cared for IV) where I would play the game for 30 minutes just to drive around, and do something insane like ride a motorcycle off a mountain, or just go exploring.