Let my do a spoiler-light take on the movie before going in depth.
It's a good movie. It's very dark and earns a PG-13; it's not something for grade-schoolers. It's as entertaining as any of the other Star Wars movies; if you liked the original three and thought Lucas was off his feed on Episodes I and II, he's back with a vengeance. It's clearly better than The Empire Strikes Back, nudges out Return of the Jedi and goes toe-to-toe with the original for best of the series.
The special effects are up to Lucas' standards; he's the undisputed master of FX and kept the bar real high. Jar Jar isn't on radar (he might have a brief no-line cameo near the end; I'm not sure if it wasn't another one of his species) and the action keeps coming.
You've got some so-so acting, but the original trilogy wasn't exactly chock-filled with Oscar-caliber performances, either. Samuel Jackson does a good job as one of the key Jedi leaders, the guy playing Palpatine gets to chew the scenery well and Ewan McGregor looks like "he could grow up to be Alec Guinness." Christensen winds up playing Anakin as angst-on-a-stick; it could have used a bit more nuanced, but it worked OK.
Of course, Yoda steals the show; nothing's neater than seeing our little green friend kick butt- "Not if anything to say about it, I have."
I don't see the left politics as much as the early Blogosphere conversations suggested. The one key lefty factor is Padme, who went from a woman of action willing to undertake "aggressive negotiations" with an enemy to a brooding diplomat/distressed damsel. In Episode I, she channeled Rummy; here, she channels Joe Biden. After Episode I, Natalie Portman was the dream girl of quite a few righty bloggers; while she's sexier in Sith (not that sexy; the outfits are merely way more feminine and the script is G-rated on that front), Padme's much less attractive here.
You have an all-purpose metaphor in where they trash an empty Senate chamber in the process of a good-versus-evil battle; when that fight started, I whispered "the nuclear option." You can pick what modern politicians are the good guys.
Here's my take on what metaphors can be lifted out of Revenge of the Sith. There are spoilers here, so if you want a clean take on the movie, don't read on.
OK, here come the spoilers.
If you haven't been in a cave for thirty years, you'll know that Anakin turns into Darth Vader at the end of the movie. The kicker is what tips him over to the Dark Side. He's cocky, ambitious and resents being treated like a kid by the Jedi Masters, but Padme's health tips him over the edge. Nightmares of Padme dying in childbirth draw him to some of the healing powers that only the Dark Side can offer; Palpatine used that as his Dark Side sales pitch.
Embryonic stem cell research, anyone? Using the promise of the Dark Side to save lives; that's very attractive. However, Anakin has to kill lots of people to try and save his woman.
Once Palpatine brings Anakin over, he beings to wipe out the Jedi, getting soldiers to frag the Jedi in battle; an extended sequence of Jedi fraggings is a gut-wrencher. A little Biblical nod is that the code for the fragging is order #66. Kenobi manages to escape by the skin of his teeth. Like Beamer and friends, Yoda's would-be fraggers are a few minutes late; Yoda is onto #66 and dispatches them before they can do any damage.
Anakin's rite of passage as a Sith Lord is to go to the Jedi temple and kill off all the child Jedi-in-training; there aren't any actual shots of him offing the kids, just him pulling out his light saber and cutting to another scene. He has to kill innocent kids in order to gain the healing powers he seeks; if that ain't a ESCR metaphor, please tell me what is.
If we can extend the ESCR metaphor a notch further, Anakin's "research" fails. Padme essentially dies of a broken heart after seeing Anakin turn dark, giving birth to Luke and Leia before dying. From what has been seen in the early going of research, adult stem cells seem to have far less negative side effects than embryonic ones. The taking of life needed to get the embryonic ones seems counter-productive and starts us down a dark path of taking lives in order to save others.
OK, now that I've spun Sith against the left, let me lob a stink-bomb in the direction of the right. From a Christian perspective, you can look at this as a cautionary tale about some of the heresies that can flow out of the quest for spiritual power
There are a lot of Christians that are drawn by the supernatural power of the Holy Spirit that doesn't exist in garden-variety evangelical faith. If people aren't careful, Satan can twist that desire into demonic activity.
On the theological left, people can be led into New Age thought, abandoning a personal God for impersonal mock-ups of The Force. On the theological right, you can see Pentecostals and charismatics so driven by healing and prophecy that Satan can false-front things, drawing people away from the Holy Spirit by errant mock-ups of the real thing.
Both sides echo Palpatine's sales pitch to Anakin; the church isn't telling you all that the spiritual realm has to offer. It is correct on one level; most churches pull their punches on what the Holy Spirit can do in people's lives. However, that extra power requires discernment on what's of the Holy Spirit, what's the Devil's work, and what's last night's burrito talking.
If we go after it for selfish reasons, we can be drawn by the Dark Side; even a seemingly-noble love of one's wife can be morphed into selfishness if one puts her life ahead of God and one's fellow man.
Here's a question for the "Spirit-filled" members of the Peanut Gallery. Are we "seeking the greater gifts" for expanding God's kingdom, or are we doing so to have a spiritual Tim Taylor ("More power!") tool kit?
If it's the latter, we might have Palpatine whispering in our ear.