While I mostly agreed with CO's post (and glad to see he's back!), I wouldn't go so far as to say that ROTJ doesn't have any "it" moments. It does... it's just that they're all located in the final act, rather than the previous movies that have really good moments throughout. As much as I love Leia in that bikini, she simply can't carry the entire movie up to its climax (yeah, I'm stepping knee-deep into innuendo, I know). Everything leading up to the final act is meh (with the first act being less than meh), and only the last half hour or so really lives up to Star Wars standards. There's Luke briefly giving into his anger and then paying the price for not carrying it out, and there's Luke and Lando barely escaping from the Death Star in the nick of time. Those moments work for me every time, and they're spectacular payoffs. However, they just don't save the rest of the movie from getting bogged down in itself. And like others have pointed out, that doesn't make it bad (except for Luke's stupid plan at Jabba's palace, which is just horrible, but even that took me over a decade to realize). There are many genuinely good moments all throughout ROTJ, but until the end, it's just lacking that spark that the other two had, and that's an opinion I've carried (although not always been able to articulate) ever since my first viewing of it when I was nine.

EDIT: Heh, it looks like I may have coined a phrase by referring to the ROTJ lightsaber as a whiffle ball bat! Yay!