Spoiler review of Serenity, the Firefly movie. Don't read unless you know or want to know what happens.
In general, it was good.
Serenity was a little bit too science fiction and much less of a western, which actually kind of disappointed me. I liked the balance in the television show, which was not present in the movie. Aside from the presence of the characters, the movie didn't feel like the TV show at all. The movie used a very cold, metallic blue filter through the entire picture, and not the usually warm firelight glow the television show had. They were obviously pandering to the science fiction audience, as is evidenced by the environs they were in for the rest of the film.
The opening moments were not particularly strong, through did the important thing of infodumping the audience on the basics of the Firefly 'verse and reveal to the audience exactly what happened to make River Tam into a "psychobitch" as my roommate Evan not-so-fondly terms her.
Malcolm and Simon begin the movie very out of character. Mal goes so far as to basically imply that the Tams are not part of his 'crew' which from what we've seen in the series absolutely untrue. This is unfortunately consistent with Joss Whedon's inconsistent characterizations during the course of the series, most notably in episode 10's "War Stories" where Wash suddenly develops a burning jealousy for the relationship between Zoe and Mal. Malcolm understandably starts this way, because as the main character he must develop during the course of the movie in order for it to be a good movie, therefore his character must be set back a little bit from the development he had during the course of the series. Simon is out of character a good portion of the movie, and was too similar to Mal to be able to stand on his own.
The movie also had too many one-liners. Two or three in the course of a television show is enough, but the movie had too many and the setups felt fake Those of you who had hopes that one day Zoe and Wash would have the beautiful child they promised each other in "Heart of Gold" will be disappointed because Wash dies. Pity, because he was my favorite character. ._. But they handled his death very well and especially Zoe's reaction to his death.
Those of you Kaylee/Simon fans will be happy. There is some small resolution to the Malcolm/Inara tension, though not too much. Shepard Book dies without you ever finding out what he used to be, which is the only disappointment.
The fight scenes with River Tam are well choreographed, though you can tell by the speed of her movements that she isn't naturally a fighter. There are moments when the movie will have you on the edge of your seat (Wash's amazing flying through a battlefield riddled with Alliance/Reever crossfire) and there will be moments where you laugh...well, maybe not because most of the good oneliners are already in the trailer.
The new characters Whedon creates, are quirky and vibrant, all save for The Operative which we see the most of because he's the movie's mistaken villain. I prefer Mr. Universe out of the new faces Whedon has brought to Firefly, but watch out for his creepy robotic Real Doll/Wife. I always knew that eventually they'd come out with something to satisfy the couch potato/hacker in everybody.
Serenity is a fun ride, and I can say that with confidence 'cause I am neither a Buffy fan or a Whedon groupie. Firefly fans will enjoy the movie, other will perhaps not understand everything going on, but if they enjoy a good ride they'll like it nonetheless. Not entirely up to par as a feature film, it's satisfying as a closure to the Firefly universe. Hanging threads are resolved, and there's enough left at the end for you to know that the crew of misbehaving miscreants under Captain Malcolm Reynolds keeps doing what they do best--smuggling shit and getting themselves into shitloads of trouble. Vaguely reminiscient of the way ST:TNG ended, the Firefly crew just keeps on truckin'. And hey, the heist at the beginning goes rather well, so maybe they won't be worried too much about running out of gas or rations in the near future.

I think most of the problems were pretty much attributable for it being a season's, maybe two season's worth of plot in two hours.
I hope it'll do well enough to warrant some sort of continuation, because I still want explanation for the blue-gloved dudes.
Yeah, I did want to see who those blue handed dues were, and I wanted to know about their head 'splody device. :/ I'm so sad the show got cancelled. And you know...that WASH DIED. ;_____;