First, the good: Ewan McGregor. The best thing about the prequels. And for ROTS I think he really hammered it home; I believed him to be Obi Wan (despite the numerous plot holes about his memories, lies, etc). I was moved by his final scene with Anakin. That scene will be the reason I go to see the movie again.
Christopher Lee was criminally underused. He had potential (although making him Qui Gon's master/Yoda's student was stupid an unecessary). JB and I have exhausted our complaints of his role in the third movie so that is enough for now, excepting that I wanted some closure with a character that Lucas at least made an attempt to develop (unlike Darth Maul).
Effects in the third episode were good but started to feel like the Matrix sequels. That is, it was more like Lucas showing effects off rather than using effects to accentuate action sequences.
Second, the bad: Foremost, I was wholly unconvinced of Anakin's turn to the Dark side. There was no temptation as hinted at in later movies. Just lies. Anakin is not a tragic figure in the sense that we pity him; no, we identify with him. Essentially he is forced to choose between saving his wife (partly to atone for his mother's death) and....what?? The Jedi? They are jerks to him. On a side note, I was much more impressed with Hayden Christensen's acting this time around, perhaps only because it was so bad in II.
Now I've upset myself. Aside from that major thematic flaw, there are so many plot holes and inconsistincies that I don't even consider these movies to be part of IV-VI. Honestly, I was able so set up some sort of mental block prior to I so that I can still watch and enjoy the later movies without even thinking about the prequels. It makes me sad that that is what I have to do.