I just got to Trevor too and I must admit his missions have been the best, although I think I prefer Michael and Franklin personality wise.
Surprised there isn't more discussion happening in this thread.
I'll do a little positive/negative thing:
Positives:
3 characters just breathes a massive fresh air into the story. I often find myself pondering who to use next, just to check what they've been up to really.
Driving. A big step up from IV.
The world. Amazing.
Great cars everywhere.
I could go on and on with the positives but I think we all get it.
Negatives:
Random occurrences don't happen often enough!
There aren't reasons to explore around. There's barely any collectibles (50 space parts and 50 scrap papers). I just wish there cash stashes, upgrades or even weapon cases to find scattered around the world.
Takes a little too long to lose wanted level.