Both "Star Wars" prequels -- "The Phantom Menace" and "Attack of the Clones" -- received A- grades from me. I was so caught up in the thrill of the films, by the technical wizardry and imagination, that I didn't notice, at first, the deep flaws in the acting and the dialogue.

In both cases, on subsequent viewings, I realized I'd been wrong. An A or A- review, in my philosophy, should be for films that will stand up to repeat viewings. Those first two "Star Wars" prequels were full of dull scenes when I watched them again, and the hackneyed dialogue, overlookable the first time because I was so excited to get the story that I didn't notice how badly it was being phrased, became painfully, embarrassingly obvious. Had I been more circumspect when I first saw them, I'd have given them B's.

I tell you this because I've given "Episode III -- Revenge of the Sith" a B+, and I want you to understand that it's better than its predecessors, their on-the-record A- grades notwithstanding. I've already seen "Revenge of the Sith" twice, and it certainly stands up to repeat viewing better than they did.

This is the grim movie, as you know, the one where Anakin Skywalker (Hayden Christensen) turns to the dark side and becomes Darth Vader. The one where Luke and Leia are born and handed off to their respective foster families. The one where the evil Emperor of "Return of the Jedi," known as Darth Sidious, makes his presence known and establishes his empire. The one where nearly all the Jedi are killed.

Those aren't spoilers; those are things we know from seeing Episodes IV-VI. And it's good that we've seen those movies, too, because Episode III itself offers no hope for the future. Evil wins in Episode III, and good is defeated. Were it not for our knowledge of what is yet to come -- the emergence of Luke Skywalker as a hero who defeats the Empire, and so forth -- Episode III would be the most thoroughly downbeat movie this side of "Seven."

I give George Lucas credit for making the film the way it needs to be made: darkly, and with little silliness. R2D2 has a couple moments early on (the droid seems to develop new powers with each prequel), but for the most part the mood is intense and serious. Lucas was apparently so intent on striking the right tone that while he allows the buffoonish Jar Jar Binks to be visible briefly (in scenes where it makes sense he would be present), he does not let him speak.

In Episode III, the noble Republic is at war against separatists, a radical group helmed by the Sith practitioner Count Dooku (Christopher Lee). His top commander, an evil android named General Grievous, has kidnapped the Republic's leader, Chancellor Palpatine (Ian McDiarmid) -- an ironic undertaking, given that Palpatine is secretly as anti-Republic as his abductors are. (Actually, it might be more accurate to say that Palpatine is not anti-Republic but pro-Palpatine, his eyes on the eventual prize of turning the democracy into an empire, with him at the head.)

The Jedi, friends of the Republic and of democracy in general, agree to rescue Palpatine from Grievous and Dooku. Obi-Wan Kenobi (Ewan McGregor) and his junior partner Anakin Skywalker (Hayden Christensen) are the rescuers, and the act solidifies Anakin's burgeoning friendship with Palpatine.

Anakin is still reeling from the death of his mother in Episode II, and he's begun to have premonitions that his pregnant wife Padme (Natalie Portman) will die in childbirth. Since Jedi aren't permitted to marry, Anakin can't even tell Obi-Wan that he and Padme have wed, let alone that he fears for her safety. Palpatine learns of it, though, and he lets on that while the Jedi would never teach Anakin this, the Sith have certain powers over life and death. Obi-Wan is still Anakin's teacher, but Palpatine is fast becoming his true mentor. And not for nothin', but the Jedi Council is growing suspicious of both Anakin and the Chancellor....

The "Star Wars" films are often called "space operas," and that description has never been more apt than with "Revenge of the Sith," a sad film whose hero is seduced by wickedness as tragically as Othello and Macbeth were. If only the dialogue were as rich as the ideas! Christensen and Portman, both able actors in other films, are still hamstrung by Lucas' flat, unoriginal lines. "You're so beautiful!" Anakin tells Padme in one of their several scenes alone in their Coruscant apartment. "It's only because I'm so in love," she replies. "No!" he says. "It's only because I'm so in love with you!"

And my favorite, uttered by Padme during a moment of stress and apprehension: "Hold me, like you did by the lake on Naboo -- so long ago, when there was nothing but our love." Where does Lucas GET this stuff from? Does he transcribe the lyrics from his Backstreet Boys albums?

He knows his action, though. The light saber duels are plentiful in this film, some of them more slam-bang exciting than others, but all of them technical marvels. And new creatures are created by the shipload, including a reptilian beast that Obi-Wan commandeers to help him fight with Grievous. (Fantasy nerds, rejoice: The "Star Wars" series finally has a dragon in it.)

The stand-out performance is by Ian McDiarmid, who has mountains of screen time as Palpatine. McDiarmid, with his upper-British accent and high manners, is ripely, chewily evil as the insidious Palpatine, delivering his B-movie dialogue with just the right over-the-top gusto. You can hardly blame Anakin for being led to the Dark Side by him; the way he speaks, with his subtle lies and manipulations, he could talk anyone into anything.

McGregor is better than nearly everyone around him, too, able to parse his lines fluidly and naturally (though, granted, he doesn't have to machete his way through any love scenes). If the tender moments between Anakin and Padme are lame enough to detract from the film, Lucas finally gets it right in the finale, where he ingeniously combines the action, characters and emotions involved in Anakin's climactic battle with Obi-Wan. This is thrilling, goose-bumpy stuff, and it culminates in what may fairly be described as the most anticipated film moment of the year: the creation of Darth Vader.

I won't reveal much about that scene, except to say that it is just what you want it to be: that mask, that breathing, that voice -- the birth of one of filmdom's great villains! Even a passive "Star Wars" fan such as myself is gripped by this scene, shot, acted, scored and edited to perfection.

It's hard to compare "Revenge of the Sith" to the other five movies because it's so unlike them. It has fewer major characters than its brethren, not to mention fewer subplots and less levity. And it's almost exactly what it needs to be, a powerful middle film to end one trilogy and presage another. It's impossible for any prequel to be as good in our memories as the original trilogy was; technology, culture and the movie-going experience have changed too much since then. But "Revenge of the Sith" is the best of the prequels, and a worthy successor to the "Star Wars" legacy.

Grade: B+

Rated PG-13, a lot of action violence, a couple fairly gruesome images

2 hrs., 20 min.