I love flipping through these.
(Make sure to check out the gallery for Star Wars as well, it has a bunch of really interesting changes (accidental public hair and part of a laser in the wrong spot among other things)) .
ROTJ had that awful Jedi Rock-music added and that sand monster. The most known change is probably the ghost of Anakin. Hayden Christensen or Sebastian Shaw?
If you're new to the Star Wars saga and watch them in the order 1-6, you'd probably appreciate seeing Hayden again at the end. But even then, there is a few years between Episode III and VI, Anakin would've grown up in that period, so wouldn't it make more sense that you should see a older Anakin at the end? That's the idea I subscribe to.