A terrific cap to the shortlived and little, but passionately, loved show Firefly.
It manages to be a neat introduction to the cast (though some fall a touch by the way side each if given a character moment) whilst also deepening personalities.
The increased budget (though by no means huge in movie terms) allows for some intense exciting action beats, with Whedon taking full advantage of the screen (a lot of his teevee stuff had cinematic qualities anyway) and Fillion and Glau, ostensibly the leads in this ensemble, make for an interesting unusual pairing and radiate charisma. Chiwetal Ejiofor exudes confidence, grace and charm and gives lie to the old trope that villains do not know they are villains brilliantly.
It is exceptionally funny, more so than most comedies, but that does not undo the dramatic stakes and a couple of well positioned (though somewhat controversial depending on who you are talking to) deaths give cost to the stakes and gain the climatic battle a tension fairly unusual for the genre.