I think where Assassin's Creed is concerned, and games like it, there's a interesting debate to be made on when a game stops merely having RPG elements (i.e. stats) and starts becoming an RPG, I don't know the answer myself but I'm disinclined to include Assassin's Creed in there yet.
As for what is and isn't mainstream, I consider something mainstream when even third-parties have a frame of reference where it's involved. Everyone can recognize a reference to Star Wars, or when it's tropes are being used or parodied, whether or not they've seen the movies but when THAC0 or Armor Class is used in a joke in a show like Futurama, at the time it was a inside joke to nerd-culture, now I'm not so sure, I think it's still borderline. But who am I?
