Dialogue was much better overall than Ep. II. Not a lot of cringe-inducing moments.
Acting was more natural also, particularly from McGregor. I think the actors realized this time that they weren't going to be directed all that well, and if they wanted decent performances, it was up to them. McDiarmid was a bit over the top on occasion as the Emperor, but still creepy with that occasional Emperor smirk he had in ROTJ.
General Grievous is stupid. Lame non-villain. All filler, no meat. That's all I'll say about that.
Hearing Vader breathe through the mask the first time was cool. Hearing him talk wasn't. His dialogue was dull and wimpy, as if James Earl Jones channeled Christensen. Jones' voice, Hayden's attitude. It's not the powerful Vader we know from the OT. ROTS still isn't enough to convince me that Christensen's Anakin was capable of becoming Vader in any way except for his weakness against the dark side. And he turns SO fast when the time comes.
I think the best thing about ROTS is that it demonstrates there are gray areas in the Force; it's not as simple as light side/dark side. You'll see high-ranking Jedi performing questionable actions in the name of the greater good. You'll hear some characters question the motives of the Jedi, and it makes sense. You'll know that arrogance runs rampant on all sides. The deepest hurt is when two of our most beloved Jedi both admit failure.
From a technical standpoint, it's a superb production. The presentation I saw was film-based, but even still, it's obvious that the HD cams Lucas used this time around are a marked step forward compared to AOTC. Very film-like. The CG is also quite good. Much more detail than AOTC, giving objects a more organic quality. I still prefer the puppet yoda from ESB to the CG version though.
The best of the PT, and better than ROTJ I think. Definitely worth seeing.