Well, I actually liked GTA3. Note I wrote liked not loved. It was a good game but not my favorite. As for Vice City...ugh, I just can't get past all that 80's crap. And Rockstar's reach exceeded their grasp, as evidenced by the glitches in the games and the problems with graphics not keepng up with the game.
Anyway, as for True Crime, well, if it's as good as Activision is saying it'll be light years beyond any GTA game period. But that's probably being too optimistic.
Still, even if it only delivers on half of what's been promised it'll probably still be better than GTA. Branching missions, the combat that's already been alluded to, and incredible graphics sound really cool.
I am a bit worried that, like I said with Rockstar, Luxoflux's reach may exceed their grasp and they may create an engine that, again like GTA, pushes the systems too far and results in the same stuff you see in GTA (walking on water, being able to see the stick dimensions of buildings occasionaly before the rest of the building appears, pop up, being shot through walls, etc.)
However, they have been working on this game for at least a few years so hopefully that won't be the case.