-Episode I - Not a terrible film but horribly mediocre compared to the rest of the films. The fact that it's related to Star Wars gives it a few extra points. It's still better IMO than a lot of other crap.
-Episode II - Some parts of this movie I really like while others fall completely flat. The Phantom Editor's version of this redeems the film almost entirely for me. I wish the scenes at Padme's parents house had stayed in. Also, no matter what anybody says, I like Yoda's lightsaber duel. The Yoda we see in Empire has spent 20 years in alone in a bog contemplating everything that went wrong so he's going to be at least a little different.
-Episode III - Good overall but suffer's severely from dragging on way to long in places. The whole opening, the duel, the expedition to stop Grievous...pointless filler. A few cheesy lines still but not a enough to ruin the experience for me. I liked the Yoda/Sidious duel, however, I feel it should have maybe taken place earlier in the movie so that it wouldn't interrupt the Anakin/Obi-Wan duel. Maybe Yoda attacking him could have been part of the catalyst for Palpatine to accuse the Jedi of treason or something.
-And I still say that watching the prequels and knowing the story makes Return of the Jedi a much better film once you know more about Vader and Palpatine.