"Attention! This is the Captain! We might experience some slight turbulence...and then explode." - Captain Malcolm Reynolds
If you've been waiting for a long time to see Captain Mal Reynolds get upset enough to utter the words, "I. Aim. To. Misbehave.", and take on the Alliance again, you'll enjoy the movie. This synopsis is from the official site:
...The film centers around Captain Malcolm Reynolds, a hardened veteran (on the losing side) of a galactic civil war, who now ekes out a living pulling off small crimes and transport-for-hire aboard his ship, Serenity. He leads a small, eclectic crew who are the closest thing he has left to family - squabbling, insubordinate and undyingly loyal.
When Mal takes on two new passengers-a young doctor and his unstable, telepathic sister-he gets much more than he bargained for. The pair are fugitives from the coalition dominating the universe, who will stop at nothing to reclaim the girl. The crew that was once used to skimming the outskirts of the galaxy unnoticed find themselves caught between the unstoppable military force of the Universal Alliance and the horrific, cannibalistic fury of the Reavers, savages who roam the very edge of space. Hunted by vastly different enemies, they begin to discover that the greatest danger to them may be on board Serenity herself...
I've been struggling to figure out how to describe the movie without giving away too many surprises - some are absolutely hilarious and some are sure to shock many fans (although there are also some very predictable outcomes). If you've never seen Firefly, you'll enjoy the movie. If you're a fan, you'll love the movie.
The first half and last quarter of Serenity are amazing. A combo of Blade Runner, Empire Strikes Back, and Aliens. The rest is back story for the non-Firefly-aficionado. You needn't have followed the series to understand what is going on or enjoy the different relationships of the crew.
What will you see?
The Captain - He's, well, unpredictable...what I can tell you is that each time I wanted the Captain to kill the bad guy, he didn't. And when I wanted him to let certain ones live, he didn't.
Jayne - Has more than his usual allotment of one liners. While his propensity for saving his own skin is hilarious, he risks his neck often enough to make you wonder if his callousness is feigned...
Inara - Gotta love Inara. When the Alliance Assassin coldly claims that Captain Reynolds will never succeed in evoking anger in him, Inara whispers from the corner, "Just give him an hour."
Kaylee - Very enjoyable in this movie. In fact, her line at the end of the movie during the Serenity Crew's most desperate battle will go down in sci-fi movie history as one of the best.
Wash - While flying Serenity expertly through an enormous space battle, evading fighters and destroyers, dodging space mines and laser blasts, Wash tells himself quietly, "I'm a little leaf on the wind." Wash is one of my favorite characters.
Doc - While the Captain and Jayne don't have much respect for the doc, he's tougher than you thought.
River - Weird chick. Really, really weird. And, you know, she just never goes crazy at the time when you really need her to...
Then, there's the Reavers. The Reavers are actually central to the plot so I can't say much other than you'll see a lot of them (hence the "Aliens" ref at the beginning of the post).
All in all, Serenity is a great movie for sci-fi fans and regular movie-goers alike. While it couldn't have possibly answered all of questions you have about the characters, it does wrap up a few plot lines.
Serenity certainly lives up to it's hype.