Yes, this is loaded with spoilers. Stop reading now. Or better yet, read it, and don't see the movie.
I won't say much. I'll point out that it takes a very, very dedicated brand of hamfisted writing/directing to make Sam Jackson and Ewan McGregor look like bad actors. I don't blame George Lucas for Hayden's bad acting - the kid clearly has no talent. His excruciating timing, frozen facial expressions, and awkward gesturing are something right out of a high school play. The kind of play where there weren't enough boys auditioning so even the male leads are unwatchable. Only in this case, there were certainly plenty of boys to choose from, so it's a mystery how this block of wood ended up with one of the most sought-after movie roles of all time.
There are too many bad things about this movie to list, and I'm sure others are doing a more thorough and better job of it elsewhere on the blogosphere. But let me just say that the "Frankenstein's monster" scene, where Darth Vader, in his very first moments as more-machine-now-than-man, breaks free of his (apparently purposeless) wrist and ankle schackles, stumbles two steps forward, raises his fists and screames "NOOOOOOOOOOOO!", was like watching my first-born child being slowly stabbed in the eye with a shard of glass. A shard of glass with, like, poo all over it or something.
So I have a choice. I can either let Darth Vader - always my favorite movie character, ever since I was a wee one - be inexorably ruined in my mind by the cash-in prequels, or I can simply decide that Episodes I-III don't count, that fans of the original films still get to use their imaginations and come up with their own versions of the events leading up to the fall of the Republic and the rise of Darth Vader, and Sean was correct in his assessment that the prequels are nothing more than elaborate fanfiction that happened to be written by George Lucas.
My destiny lies with the latter.