I'm not saying ROTJ doesn't have its flaws, and I know I'm biased cause I loved it as a child.
However, putting it together with the prequels is too harsh. ROTJ has heart. ROTJ has some emotions, something the prequels completely lack. The duel, when Vader is taunting Luke that maybe Leia might join the dark side and Luke loses it, is one of the most powerful moments in the trilogy, no scene in the prequels can even come close.