Revenge of the Sith is undoubtedly the best of the 'prequel' movies, but that's like saying that cabbage tastes nicer than sprouts. There is still a mammoth gulf between this film and the original Star Wars movies.
There is, however, much here to enjoy. The tone is much darker than any of the other five Star Wars movie, and includes numerous dismemberings by lightsabre. Indeed it's a surprise that it wasn't slapped with a 15-certificiate. The visual effects are also an improvement over the previous two instalments, with the CG spaceships and characters actually looking almost real (although that creature that Obi Wan rides looks utterly ridiculous). There are some good lightsabre duels and action sequences, and it's great to see the Wookiees again, although their involvement is disappointingly brief. The acting is also a notch better, with Ewan McGregor and Ian McDiarmid both in good form. Natalie Portman is also more convincing this time around, although Samuel Jackson is spectacularly wooden. The movie also sounds great, thanks to another brilliant John Williams score and Ben Burtt's sound department.
But then there are the flaws. For one thing the plot is far too busy. The original Star Wars movies were beautifully simple, but Revenge of the Sith, as with its predecessors, is a mess. The characters spend the movie darting about from one planet to another, with the result that the film feels awkward and disjointed. If the original films might be described as taking a trip on a recently resurfaced motorway, Revenge of the Sith feels like driving on a concrete road in a council estate that hasn't been repaired in years.
The movie also suffers from too many silly moments. I've already mentioned the ridiculous creature that Obi Wan rides, but there are plenty of other examples. Personally the sight of Yoda engaged in a lightsabre duel cracks me up every time, and for me the epic scrap between Obi Wan and Anakin is ruined by the sequence with them battling it out while perched precariously on pieces of metal junk floating on the lava river (actually I thought the backdrop to the duel was totally unconvincing anyway).
While the dialogue is better than in the previous two movies, there are still plenty of clunky moments, notably whenever Anakin and Padme get touchy-feely. However what I also found annoying was the inclusion of catchphrases from previous movies (e.g. "Here's where the fun begins"). This was totally unnecessary and I can't help wondering whether this was a desperate attempt by Lucas to make the audience connect with the original trilogy.
There are also countless plot holes. Why doesn't Obi Wan remember the droids? Why erase C-3PO's memory but not R2's? And why leave Luke with Owen and Beru - wouldn't that be the first place Vader would look for him?
However, the biggest problem with Revenge of the Sith is Hayden Christensen. He is undoubtedly better here than in Episode II, but most of the time he still comes across as a sulky teenager, and his fall from grace fails to convince. It is impossible to believe that this bland youth becomes one of the most memorable and menacing screen villains in screen history. And considering that is what this trilogy is all about, that's a fairly major flaw!
The final few scenes of Episode III, though, are great, with Vader and the Emperor on the bridge of the star destroyer looking out at the Death Star, followed by the scenes on Alderaan and Tatooine with Leia and Luke delivered into the care of the Organa and Lars families. And the very last moment, with Owen and Beru watching the twin suns of Tatooine setting behind the horizon, really make the hairs stand up on the back of your neck. If only the rest of the prequel trilogy had been like this...