Nobody's mentioned my one quibble, so maybe I'm just not understanding the movie.
The way I see it, when they're heading to Mr. Universe's hideout, there's two possibilities:
1) They don't expect to be intercepted by the Alliance; or
2) They expect to be intercepted by the Alliance.
If #1, then why on earth do they lead the entire population of Reavers toward Mr. Universe's planet? That's suicide!
If #2, then why on earth do they even bother to go there? Surely if the Alliance gets there before they do, Mr. Universe is going to be dead and the facility is going to be destroyed.
It seems like the logical thing for them to do would be to make the appointment with Mr. Universe, then go somewhere completely different and upload the video to a couple dozen messageboards. Or, I dunno, do something not suicidal, something that has a miniscule chance of success. (It seems to me that the only way they could predict their plan's success would be if Mr. Universe had a backup facility and a Buffybot to inform Mal of the facility's existence).
Other than that, I thought it was the best SF movie I've seen since Gattaca, and ties with that movie for the best SF I've ever seen.
Daniel