I want to say it looks cartoon-y, but by that I'm not talking about the picture quality. I'm talking about the way Peter Jackson has been running the action scenes. If I'm going to see Legolas jump up onto an Oliphaunt, kill everyone aboard and then slide down the tail like he's on a skateboard, I'd rather watch a Pixar movie.
That was my big issue with Return of the King, and The Hobbit took it even further throughout that cave scene.
The Fellowship and The Two Towers had much more gritty realism about them, and didn't let the effects get out of hand. I found myself able to immerse better into those movies.