I watched Revenge of the Sith last night to finish off the prequels. I was surprised to dislike this one the most, as most people seem to think it is the best one. I think it's biggest problem is how unbelievable many parts are, for example the emperor killing three of the Jedi's that go to arrest him in about 2 seconds, they don't even try to defend themselves! Yoda again looks ridiculous leaping around, and despite most people thinking he's a great actor I thought the Emperor was also crap, he looks like a ridiculous old man waving a lightsabre around and his stupid voices and faces are really annoying. Anakin's 'struggle' with the dark side is also completely unbelievable, makes no sense whatsoever. No need to mention the "Luke, Leia" and "Noooooo!" bits, utter cringe.
Overall, I think they were a big missed opportunity. The story isn't terrible, it's just let down by a combination of terrible CGI, poor acting, too many references and in-jokes to the OT, and too much attempted humour. I think a decent editor could make a good 2-3 hour film from all three movies.