To sum it up concisely: Holy fucking shit. This is what video games should be like.
After fucking days of corrupted PSN downloads I finally got it working this evening. First thing I did was take Franklin to the barbers and make him look like MC Ride. (google him if you don't get it.) I decided to steal a car to get back to his house but in doing so got chased through alleys and streets. I eventually jumped off a bridge into the canals of Los Santos, and there was something about the detail there that blew my mind a bit. Forget the downtown skyscrapers, the "filler" parts of the city, really don't feel like it.
Fast forward past a few missions, decided to save and then cheat, to spawn a stunt plane. I wanted to fly before I went to bed for the night. First thing that struck me is how beautiful this game looks at night. Completely opposite to the blurry, sludgefest that was GTAIV. Flew past Vinewood Hills and crashed into a lake.