First of all, I must say as someone who was critical of the first two new episodes that Revenge of the Sith is very, very good.
Sure, Portman can't act her way out of a paper bag (I don't know what that means either) but she's very pretty and her dialogue was mostly functional anyway.
But other than the love story the dialogue was actually very smart, very sophistocated. I mean, listen to how Palpatine seduces and twists Anakin. Very convincing, although it seemed a little too easy to me.
But overall the special effects were not the most important part of the film, and the performances were adequate, except for Ian McDiarmid who was brilliant, and Ewan McGregor who was also very good.
There wasn't much "cute" in this film, which kept it from being horrid and eye-roll worthy. Even the little bit of comic relief from R2 was handled pretty well.
Overall, this is the movie we all wished Episode I was. If this came out instead of the Phantom Menace back in 1999 we'd all be salivating for the next two chapters (which obviously would have to focus on the 20 year interim until the events of A New Hope.
Overall, I think it was the best after Empire Strikes Back, and that includes the original Star Wars. And this one changes how I see the original trilogy - it makes the first three movies better.