I don't know, at the end of last season, Rick is doing that whole, "This is no longer a democracy" thing. I see him getting pretty dark. What I find interesting is that Rick has stayed more of a good guy in the version where Shane stays alive, and Shane kept talking about how he is willing to make the tough choices that Rick won't make in the show. Its interesting that Rick turns vicious faster when he doesn't have a vicious person to do the nasty parts for him. I think it reflects that Shane was right, and that without him Rick would have had to make tougher decisions, and Rick in the show is about to learn that. That cross-medium character analysis has been one of my favorite parts of the whole IP.
Its similar with Carl. Carl is a little more protected in the show, and watching him have a slower arc is an interesting contrast. Also remember that we know a Carl that is several seasons ahead of the shows Carl. Show Carl isn't THAT far behind Book Carl, and Book Carl has a leg up on being all hardcore since he shot Shane. Now, Carl caused Dales death, and the guilt is very different. I'm curious how this will change him, especially without his little girlfriend to keep him company
The rest...well, taste is taste. Billy and Ben's absence is a pretty glaring difference, but i'm curious how they are going to handle the difference, especially with the crazy guy at the prison. As for why they are absent...well Id guess that its because they added some new characters, and the narrative can only take so many characters. I do agree that doing a parallel story was for the best. That was a good choice, and it makes it feel like the universe is being expanded on.