Basically, Episodes 1 & 2 set this movie up. On their own, they have no particular merits. We need to see Anakin become who he becomes, but the exposition across two movies is too dull.
Yes, the acting (especially Padme and Anakin) is a bit stilted. Yes, the writing is patchy. But Lucas is a technologist first and foremost, and the action scenes are great. The pacing was uneven, which left character development a bit stilted. The characters do grow, which is a bit of an accomplishment for Lucas, but the pacing of that growth seems uneven. Yoda is awesome, and there's a scene which, if I may border on a spoiler, reminded me of the end of The Godfather.
Fans of the original 3 wanted the prequels to explain what was up with Vader, Luke, the rebellion, the Emperor, etc. The earlier two prequels pointed out where those answers would come from, but didn't tell the story the way we wanted. But this movie doesn't just tell or foreshadow the bits in between, it shows us in a way that's engaging and fun. Ms. TfK was engaged in it enough that she really wanted Anakin to be good, and not descend into the evil of Darth Vader (an evil we know to be limited because of Episode 6, "The Return of the Jedi"). For Ms. TfK to enjoy anything about Star Wars is quite an achievement.
I'm revealing nothing unexpected in saying that the payoff is the battle which turns Anakin from a twentysomething with a chip on his shoulder into the vinyl encased monstrosity that is Darth Vader. And I'll reveal nothing more, except that it isn't a disappointment.
That's a major step forward from the previous two.
If it weren't Star Wars, it'd be a mediocre SF flick with some dumb logic, like when someone says of Luke "We'll send him to live with his relatives." (Why? Why not send him anywhere but to his relatives? Some questions apparently do not need answers.)
But it is Star Wars, and the magic is back.