I feel this way towards all of the PT movies, I love some stuff and absolutely despise other parts of the movies. I think this quote will help you understand why all PT movies are so uneven, and I think it had to do with Lucas doing EVERYTHING on these movies instead of more collaboration like the OT:

"I went up and met with George at his house, and he introduced me to a lot of the people working on ESB. Then, when the initial draft script came in, we weren't happy with it. So we started meeting with Larry Kasdan and re-working the script, and we all threw in ideas. I kept thinking in terms of characters, George was thinking a lot more of the actual story, and then Larry Kasdan was thinking dialogue, which ties in with characters and story. We worked for many weeks, and finally got the script."
-Irvin Kershner talking about the pre-production of ESB in 1979 (Star Wars Insider, June 2000, pg 26.)