My only gripes with the special effects after all these years are:
1) The boxes around the ships..grey is more appropriate than white..most of which was cleaned up in the special editions.
2) The Rancor scene always sucked and was never cleaned up.
3) The black splotches around palpatine's face (very annoying)were never cleaned up which never made any sense.
Not much really. I didn't like several things about ROTJ, but honestly that's Lucas' problem with story..not a special effect.
Honestly, Why doesn't lucas just recast and reshoot the entire first trilogy and call it a remake? He could make big money and redo everything.
