Here is my first warning: Miss this movie. Give it a pass, let it walk on by. If you're desperate to see it wait until it comes out inevitably for download in a few days, but don't give Joss your hard earned $7.50.
Here's my second warning: After this paragraph, I'm going to explain why. It'll contain spoilers. Big ones. Read at your own risk.
Again, AVAST MATEYS, THERE BE SPOILERS AHEAD!
Let's start with the good. The flying sequences are ruling. The writing is the same as the show, the quips just as funny and nearly every character is done justice in this film. Some, more than others.
First of all, from this point on, this movie shall no longer be referred to as "Serenity." It is, forever more, "River the Vampire Slayer." The entire movie is focused on River without ever giving anything useful away. Yes, you find out River's big mission, and hey, it turns out all she needs to do is go to a planet and boom, schizophrenia is gone. Turns out her craziness is not a result of the tests done on her, but just because of something random she gleaned from a member of the Alliance's parliament. The Vampire Slayer part is because after this, the series is officially about River. Joss made it VERY clear that no one else matters. And believe me, she acts like Buffy the whole movie. Buffy on crack, but Buffy nonetheless.
The other loose ends? The big ones like the hands of blue guys and book's past? No mention. Well, Book does get a few minutes of conversation before he dies. That's right, dies. Book is blown to hell because the Operative wants to get to Mal, in the second most pointless death in the movie. The first belongs to Wash. That's right, Joss kills Wash off in this movie. In case you think I typed it wrong, here it is again: WASH. DIES. In a stupid way, too. He's in mid quip after having saved all their lives when a wooden spike is shoved through his chest. Hmm. It's such a shock value death that none of the cast, for the rest of the movie, even bothers to mourn. They spend half a second less on him than the .5 seconds they spend on Book. Dumb, dumb dumb.
Parts of this movie are gold, but pointless killing of good characters for shock value? That's a slap in the face, Joss. Thank you very much. I think it's just that whenever he gains full creative control Joss decides to mess around, just to prove a point that the world is a sucky place or something like that. Stupid motto. When he's on a place that reigns him in, with a team of other people helping make his ideas good, he produces gold. When he's alone, he does stuff like this.
I've forgiven Joss several times before for boneheaded decisions. This is the last time. Firefly, Angel, and Buffy seasons 1-5 and the first half of Astonishing X-men will always be in my heart as great stuff. But I'm done trusting the man to produce any sort of follow-up that I'll enjoy.
In other words, as far as I'm concerned, this movie doesn't exist. Wash and Book are alive, and everyone is in limbo from where Objects in Space ended until someone gives me something worthy of being a continuation of that series.