1. The game is slightly dumbed down. Poor vehicle physics (vehicle damage system not sensitive enough, vehicles fly like if they were made out of solid paper), missions are to scripted
tbh I think the main reason the physics are a little dumbed down is because of people complaining that GTA IV driving was "no fun". So the devs were doing fan service.
And about missions being too scripted, when have they ever had more freedom? I remember in San Andreas a chase mission where I HAD to use the scripted vehicle, or there was one where I would HAD to win the race (I wanted to just kill all competitors). In fact GTA V missions allow more freedom because of the heists having multiple approaches.