A lot has been said here already but just to pile on - I love John Williams' scores for Star Wars, probably more than I love the films themselves. The scores to 'Star Wars' and especially 'Empire' are my favorites of all time, and that's including Howard Shore's scores to LOTR, which is saying a lot. And while I don't think Williams ever matches his late 70s/early 80s efforts, he's had a few gems since in Hook, Jurassic Park, Schindler's List, and Harry Potter. (Catch Me If You Can was fun, of course, but limited by the type of movie that was.)
As for the prequels...while each film introduced a great new theme or two (TPM: Anakin's, Trade Federation, Naboo, and of course Duel of the Fates; AOTC: Across the Stars, ROTS: Battle of the Heroes) and usually had a few unique, memorable cues (TPM takes the cake here) the scores as coherent entities overall suffered by poor storytelling and lackluster characters on Lucas' part. Last minute re-edits probably didn't help either - just look at how great the reconstructed TPM score is! (It's the only one that begins to approach the classic scores of yore.) Then of course, there's the fact that Lucas redid the turn of Vader in pickups - considering that such a huge story decision was done so late in the process, it's pretty amazing that the music for that scene worked just fine. (Or not. I haven't seen Episode III in a while and don't even remember if the music in that scene was relevant or simply subdued. That would never happen for the originals!) Anyway, all things considered, Williams did a pretty good job, even if there weren't many memorable cues and none of the prequels had a proper, original end credits suite.
Probably the most annoying single thing, besides the chore that is listening to the AOTC score, and the post-facto butchering of TPM, is the shoehorning in of the 'Through The Window' cue from 'Empire' into the Yoda vs Palpatine fight. It makes absolutely no sense from either a story perspective, a musical perspective, or a film perspective. By which I mean: the two fights do not parallel each other in the slightest, neither emotionally nor from a plot perspective, the presence of the music here is jarring and out of place considering what we're hearing for the rest of the film, and the matching up of the cues/beats with the characters actions in the film, which were just spot on in Empire, is nonexistent in the ROTS scene. Annoys me to no end...and you KNOW this was a conscious decision by Lucas too; it's inconceivable that Williams would be responsible for something like this. (On the other hand, it's kind of cool to hear a second 'official' rendition of that iconic cue. Still, not worth it IMHO.)
