They did a pretty remarkable job for the console versions. The main differences are pretty subtle, but you can definitely get it to look better on PC. Water reflections, texture quality at view distances, etc.
Incidentally, I DID hear something about the shadows drastically affecting the drag on your system. If you're going for higher settings, overall, than your system can really handle in a very easy fashion, you can probably turn shadows down to get a little bump in performance for everything else. Will it be enough for your specific system to run it on the settings you want? I'm not really sure.