First, let me say that I enjoyed Serenity. But I think writer-director Joss Whedon is a big baby. He originally wrote Buffy the Vampire Slayer as a feature film, but when it fizzled at the box office, he blamed the studio for screwing up his vision and then took his creation to network TV, where it became the hit he wanted. After several lucrative years writing about vampires, Whedon's follow-up show Firefly was cancelled after a dozen odd episodes. Livid, he came full circle and somehow convinced Universal's bean counters that a theatrical feature spinoff based on his dead show would be a hit, ala the Star Trek films. Hence Serenity.
I gotta hand it to the man: he's got nerve. And as it turns out, he's also got a pretty shrewd sense of what works and what doesn't. Still, he sounds like a whiny little brat.
That said, even as someone who never saw a moment of Firefly, I didn't have any trouble following Serenity's story, though I'm sure I missed out on a lot of details. Whedon jumps right in, assuming everybody's been well-acquainted with the little universe he's created, and we follow the adventures of the spaceship Serenity, with its Han Solo-like pilot and his smart-talking rebel crew right out of Aliens and/or The Matrix, as it ferries around a waifish girl who turns out to be an ass-kicking Buffy type, programmed by the Galactic Empire - er, I mean the Alliance - to be some sort of secret weapon.
If you think I'm suggesting that Whedon's ripped off ideas from virtually every successful sci fi picture from the last 30 years, you're right. Not that this is entirely bad. In fact, for fans of the genre who have been nothing but frustrated at the bloated sequels/prequels to Star Wars, The Matrix, Star Trek, Alien, and so forth, Whedon's got to be seen as something of a savior. He's a geek writing for geeks, finding the best parts of the movies he loved in his youth and updating them with both vitality and snarky teenage wit. Thus, he's managed that rare achievement: connecting with the under-30 crowd. So even if he defines his characters primarily by the schoolyard crushes they have on each other, it's a gimmick that works for him.
If you're a Firefly fan, you've already seen this movie. If not, don't be afraid of getting too lost. Though it's by no means brilliant, Serenity is still much more fun than any of the ponderous dreck that's been passing itself off as science fiction lately.