Overall, I liked it. I had the same problem with it that I had with the series episodes I've seen: the characters can be damn hard to like. Mal is not a stone-cold bastard by temperament, but he is a desperate man, and desperate people do desperate things. If I'm forced to sit and keep watching long enough to get past the wish for the ship to blow up and take these unpleasant people with it, then I like the rest of it.
Mr. Universe: I liked the character, but a pirate broadcaster who has neither mobility nor defenses doesn't have a long life, either. But mostly, I kept flashing on Ghost in the Shell. Hacker-dude-with-creepy-love-robots shows up in the original manga, and his bit of storyline got cannibalized into the second movie (Innocence). It's the love robots that are the problem, take that element out and the two characters are no more related to each other than to any other hacker secondary character. But that bit of characterization is very specific and it bothered me.
Pax: I really have to wonder how Phil Foglio is going to feel when he sees this movie. Sadly, Phil and his Buck Godot comics are obscure enough that I'm willing to believe that Whedon has never seen them and the Pax was a purely innocent coincidence. Whedon went in a different direction with it, too, but even so, I suspect it will be weird sitting there watching somebody else use an eerily similar plot device.