SheBear: To throw a bit of a wrench into the discussion: what about entirely CGI movies?
They can be glorious, but they have one of the same issue that cel-animated films have, in that everything is always planned ahead. There's no spontaneity to them, because everything was storyboarded months earlier. While that level of planning can lead to good movies, you can also miss out on stuff like Indiana Jones shooting the swordsman, or any number of incredible shots of transient light in the sky in Westerns. (And you don't get bloopers, either, unless they're made on purpose like in A Bug's Life.) CGI has its own technical limitations as well... for one shot in the Incredibles they practically had to rewrite the rendering software because it couldn't handle a character putting an arm through a hole in a shirtsleeve. Hair is also very difficult to animate, which is why it's normally in an up-do, very stylized, or under a hat. Sully's hair in Monster's Inc too AGES to animate even just for the dailies. They're also pretty damn expensive to make.
They're great because you're unbound by physical limitations, but I don't see them conquering live action any time soon.