- The action and the violence--real, bloody stuff that remains true to the idea of the Firefly-verse, rather than turning it into generic sci-fi laser pistol land. People die. People bleed. People hurt. It may have only cost 30M to make, but it looks like a 50+M budgeted movie.
- The dialogue--much like Aaron Sorkin's, Whedon's dialogue has a vaguely theatrical flare to it, but unlike Sorkin, he's unafraid to tweak that. While with Sorkin, an extremely earnest speech will be followed by applause and embraces, Whedon follows it by undermining it.
- The philosophical issues raised by it--There's a lot going on in the movie on a thematic level--Whedon has some things to say about family, love, and sin, and they're interesting, at a minimum.
- The performances--This ought to be a breakout part for Nathan Fillion, who's got the swagger of Harrison Ford as Indy Jones down to a T. Summer Glau never had much to do on Firefly other than whimper and say cryptic things, but her physical performance here is just incredible. Chitwetel Ejiofor follows up his solid villainous portrayal in Four Brothers with another one, though this one gets a bit more psychological depth.
- While most of the characters are decently, if perfunctorily, introduced, I suspect folks who haven't seen Firefly won't understand at all who Book and Inara are, and their characters are given somewhat short shrift.
- The final five minutes of the film are rushed, in particular, one character's reversal of his stance, which comes with little backing. (And where did all the parts and shit come from.)
- The "big reveal" is something I figured out half of a good 15 minutes before it was made (the Reaver part).
- Many questions aren't answered--Inara and Book's backstories, the Inara-Mal relationship, and the like.
It's still solid stuff, recommended, especially for sci-fi fans, though I'd be interested to hear how non-Firefly watchers take to it.