So, I don't watch TV, right? And I'm not much of a movie buff. Except for anything by Joss Whedon. There's reasons for that liking-of-Joss, which have in a complicated way to do with storytelling, humour, and a strong feminist slant.
But why am I telling you this? Go see for yourself. The movie is all a movie ought to be, although I wish there was more (more! more!) of it. You don't need to have seen the Firefly series first, but it'll make you love the characters even more.
Also, all the chicks kick ass.