I'm a fan of open world games, but as much fun as they are, they are also the genre that usually leaves me with the longest list of improvements. In general though, I'd like to see some open world games to go into this direction:
1. Smaller, more detailed worlds. I don't really see the point of some of these worlds being so damn big. Just more cookie cutter filler to make the travel time between objectives longer. I want an open world game that is big enough for me to get lost in the first time I play it, but I want to know it as well as I know my neighborhood by the end.
2. No hud-game maps with routes. I hate open-world games where I'm driving and instead of looking at the game screen, I end up staring at a stupid mini-map in the lower hand corner that has an route drawn on it. If your world is so complicated that this is the only way to get from point A to point B, then that means your environments are not distinctive enough and your world is probably too big.
3. Less generic cookie cutter pedestrians and more unique NPC's. I understand that it takes a lot more work but again, I'd trade the number of pedistrians in a typical open-world game for 1/10 that number if they were all unique and felt like they had a purpose instead of just a randomly generated model walking around aimlessly saying the same comments over and over.
4. Mission structure needs to evolve. I'm tired of the whole missions are given by glowing characters stuff. I want to feel like I'm in a real live world. Have stuff happen to me. Have the missions come and find me. Have me get kidnapped while I'm driving around. Have me get home and realize my home was ransacked and then have me proceed on an investigation.