As a fan of the show, it was excellent. Very much a TV-show turned movie, it kept all of the charm of the source material and wrapped it up in a big, galaxy changing sweeping plotline that answered questions from the series, but posed them in a way that I think will be accesible to non-fans.
I think, anyway. I tried really hard to watch the film as a non-fan, but it wasn't easy, and I failed. The first fifteen minutes were bumpy, and in need of some editting, but once you got through that bit, the whole thing moved fast, swinging you from honest-out-loud-laughter to sniffles and back within the course of a single scene. It wasn't jarring, but very real in this- we're-all-going-to-die-gallows humor.
Watching, I couldn't help but wonder, does Joss Whedon shit gold? He took a show that was cancelled after one season, drummed up enough fan support to turn it into a movie, made the movie in which he kills major characters and the fans love him for it.
Something I feared- the series was remarkable in that all of the space scenes were silent. When the trailer came out, I feared that they'd be putting sound in- but fortunately, it was just for the trailer, and understandable change. No fault there.
Other than that, I think, non-fans can get into this movie. But I know that they wouldn't enjoy it as much as a fan would- which means- beg, borrow, steal, or illegally download the series, and watch it. Definitely the best television made in the US in memory, and the movie is certainly looking to be the best film coming out this year for sure. It won't be in line for any Academy Awards, but you'll be hooked.
Oh, and I saw a movie poster for the next "Must-see-fanboy-film"- Wallace And Gromit: Curse of the Were Rabbit