I got to see the movie on Monday and it was all sorts of kick-ass. I attempted to watch the show when it was on Fox, but couldn't get involved. When it began airing on Sci-Fi I started to watch it, but then my cable company removed Sci-Fi from the lineup, so I got the DVD and watched the entire series. And it was just a great series that was cut short before it's time.
The movie flows just like the series, in fact like all of Joss Whedon's work. Though that could be a bit bothersome to the uninitiated, as could some of the references and/or character relationships. The movie though was definitely outstanding and certainly leaves open the possibility of sequels, as Joss was recently quoted stating he was given the green light for more movies, although he didn't specify what movies.
I highly recommend seeing the movie, even for those who never followed the series. It certainly brings back the fun aspect to sci-fi movies that A New Hope brought almost 30 years ago.
An oh yeah....
River = The Reaver SLAYER!