1. The inability to wound people by shooting at non-critical areas of their anatomy
2. NPCs killed the moment you punch them as if they've been slapped in the head by the hand of God
3. So many food vendors all over the place and you can't buy a hot dog or a burger from them
4. There are pool tables in the game, but you can't play pool
5. I really enjoyed the bowling and air-hockey in IV and disappointed that these haven't returned
6. There's a casino in Los Santos, but inaccessible, so you can't gamble - roulette, poker, blackjack, slot machines
7. There's a racetrack, which is pointless, because nothing actually happens there
8. It would have been nice if the arcade games could actually work; I enjoyed playing QUB3D in IV and the Space Monkeys (amongst others) video games in SA
9. There are fast-food outlets in Los Santos but you can't enter any of them to buy food to replenish your health
10. Buildings that are enterable during missions, but inaccessible in free roam, such as the Life Invader offices
Rockstar appear to have removed far more little details in this game than they have included which would have made the world seem far more immersive than it is.
I can only hope that IF they ever consider bringing GTA V to the next gen consoles that all these little details will be taken into consideration. It's a beauitifully detailed world, but it seems emptier to me than GTA IV.