Better layout, better index and new art, along with typos corrections and errata included. Not bad.
Well, if there's anything to be said about post-2E editions it's that the art has become better and better. That is, not counting 1E/2E art by Trampier, Erol Otus, Russ Nicholson, Roslof, Emmanuel, Easley, Elmore, Caldwell, Mark Nelson, Ken Frank, Brian Despain, ...I hated the art in the revised
I guess it's a matter of taste.