Saw it last night for the second time.
I'm a fan(atic), so I can't give an objective review, or at least the skeptics won't trust any review I give as "objective", but here goes anyway:
I really liked the plot, most of the acting, the new characters, and the action was incredibly good. I really enjoyed Anakin's scene with his mother and what followed, Yoda in every scene he was in , and the sight of so many jedi fighting in the same place. Another thing about Yoda: the scene with the jedi children contrasted nicely with Yoda's big fight scene later, while complimenting it at the same time. Very nicely done.
As far as acting, I can't recall a scene that featured really bad acting , though I remember a few where I was disappointed that Lucas didn't get a better performance. I was impressed by Anakin, Palpatine, Jango and Boba Fett, and especially Christopher Lee. Anyone who can make me take a villain named "Count Dooku" seriously is an Actor with a capital A.
Some of my dislikes: The banter between Anakin and Obi-Wan seemed a bit forced, especially at the beginning of the movie. I think it could have been done better. Overall, I liked their interactions, but there was room for improvement.
The business with C3PO toward the end would have been better without the lame one-liners. I started to wonder if I was in a film with an Arnold Swarzenegger parody. I do think the comic relief was necessary, and having threepio taken apart is a tradition,

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R2D2 can fly? I wonder why he didn't do it in Episodes IV - VI? That could have been left out. R2 is impressive because of his courage and cleverness, not because of his gadgets.
My biggest complaint is the pacing. The movie had too many scenes of the same nature back-to-back. Love-scenes followed by three more love-scenes and several political scenes followed by several action scenes isn't good drama. I agree with many others that the movie wasn't paced as well as it could have been.
One problem that non-fans (or perhaps casual fans) may have with it is that the plot is complex. To really understand what's going on can be tough, and I have a feeling that when the average movie-goer sees a film they don't understand, no amount or quality of action, acting, romance or special effects is going to make them like it.
Overall, I loved it though. I definitely liked it better than Episode I, or Episode VI. It's not the best Star Wars movie, but it's certainly not the worst. (Of course, I'll watch the worst Star Wars movie, Episode I IMO, and still enjoy it more than most movies.)
As long as your expectations aren't unrealistic, (Let's face it, it's going to be tough to top the original trilogy folks!!) I think most people will enjoy this film, and Star Wars fans will love it.