1.The crap song in Jabba's palace.
2. The emperor's line about "this is the offspring of Anakin Skywalker" The line doesn't fit Vader's reaction. In the end of ROTS, he's gets so mad that he rips his restraints off the table and pops some of the droids. If Vader found out that his son was in fact alive, shouldn't he have been more, oh, I don't know, happy ? With that line, he doesn't seem like he cares too much and not really all that surprised.
3. The stupid song at the end of Return Of The Jedi. The music doesn't really fit the action. The Naboo scene would've been alright if it wasn't for the group of Gunguns (sp?) climbing all over the roof of that building.
4. Hayden Christensen inserted in the ghost scene in Return Of The Jedi. Just dumb. I don't buy him at all as an actor.
5. The Solo/Jabba scene in ANH. Kind of takes away the grossness and surprise at seeing Jabba later on.
6. Of course, the Greedo scene. Why the hell would Lucas change this so dramatically ? It was much better when Greedo didn't shoot at all. The CG that was used to make Han jerk to the side to avoid Greedo's blast was so horrible. Ugh.