This getting a 10 isn't a suprise, it was never in doubt. On the balance of things I expect it will be an excellent game, but I too have concerns. Like Cunning, I thought GTA IV was hell to play, boring, depressing, controlled badly and ugly as sin. This *sounds* like it will be incredible, but some of the things you've mentioned concern me. The slow start, slower even than GTAIV which was itself incredibly slow and boring, that's not a good sign, it sounds like it'll be a real chore to play through the beginnings. Then there is the thing with Trevor, which concerns me a fair bit, the lack of choice to ignore a particular part because it is too graphic is a bad oversight. It's a small thing, but it bugs me that R* have chosen to include it then not let people by pass it. I personally feel R* have a duty to inform people and let them avoid the worst of the unpleasantness.
These are the only things I can see might be a concern though, the quality of the controls and general gameplay interface, the story pacing and Trevor. The rest of it really does sound rather excellent.
“It's a movie. If you are going to believe and be affected by an action film, you shouldn't go to see Pocahontas because you are going to think you are a Disney princess” Chloe Grace Moretz, what a legend.