Actually, I'm wrong. It is deep, in a sort of reptilian-brain way, but it's not complex. At their best, the Star Wars movies are deep in that, when you sit back and make a point of turning off your analytical faculties, the pure narrative of the story goes deep into your subconscious, like a fairy tale.
Back in 1977, when he reviewed George Lucas's first one, Roger Ebert wrote that it was "entertainment so direct and simple that all of the complications of the modern movie seem to vaporize." Revenge of the Sith doesn't quite have that headlong glee, but it is perhaps stronger in other ways.
Like other fairly tales, it dispenses with much realism: people talk in flat pronouncements, and some events whiz by so fast you don't have time to think about them too much (which is generally a good thing). But the final battle between Obi-Wan Kenobi and Darth Vader, which Star Wars junkies have imagined since rumours of a light saber duel on a lava planet first emerged more than 25 years ago, is better and has more power than I think almost any of us could have expected.
Looking at the whole series, it could have improved vastly if Lucas had dispensed with Menace altogether, cut down on Clones by glomming small parts of it onto into this movie, and had less of the Ewoks in Return of the Jedi. That, and he should have hired someone else to write the dialogue for the whole series, instead of just Empire and Jedi. It would have been nice to get some Han Solo, or someone like him, in the prequels too. (During Sith's first calm view across the cityscape of Coruscant, out of the corner of your eye you can see the Millennium Falcon pulling in to land. That's as close as you get.) Then again, Jar Jar Binks has only one brief shot and no dialogue, so there are small mercies.
In the world of film, the worst sequels cheapen their predecessors (and run the gamut, from Highlander 2 and The Matrix Revolutions to, yes, The Phantom Menace), while the best add resonance and understanding (Superman 2, Star Trek II, and The Empire Strikes Back). Sith is in the second, better group. Thinking back to the original trilogy, Obi-Wan and Yoda seem sadder and more wounded. Luke and Leia, and even Chewbacca, make more sense, and Vader and the Emperor are more evil.
Here's the judgment: when my 14-year-old self came out of Jedi, was I hoping that, in my future, there would come the kind of prequel-finale that Sith turned out to be? Yes I was. If you were too, go see it.