First impressions: It's quite good, good enough to show even non-anime fans. Visually very pretty, plot is perfectly adequate, entertaining yet moderately deep, it's about all I ask for in an anime movie: it's fun.
The movie is strongly reminiscent of the animated series - if you lengthened and filled out one of the standard episodes, boom, you've got a movie. All of the Bebop crew are present, which would put it, time-wise, roughly in the middle of the series. Each of them plays a significant part in tracking their latest target, a bio-terrorist who plans to unleash an unpleasant plague on the population of Mars, but as in the series, they work side-by-side but not necessarily as a team, rather as a loose affiliation of, err, cowboys. The plot is simple but reasonably compelling. The antagonist's motivations are laid out; I didn't find them particularly sensible, but, ignoring that, the actions of the characters make sense and everything pretty much holds together.
The movie is significantly prettier than the series. Instead of the computer-generated beauty of Spirited Away, there are quite a few exquisitely drawn backgrounds. Most of the action takes place in a city on Mars which bears a strong - very strong - resemblance to modern-day New York City. Shadows are rendered with great care, leading to a number of scenes where the shadows play as much of a part in the scene as the character casting them. Although the rendering of Martian daylight is not, perhaps, very realistic (Mars is going to get a lot less light than Earth, even if it's massively terraformed...), the artists do take the opportunity to show us several beautiful sunset shots. The movie is worth watching for the art alone, IMHO.
Fans of the series will know that it's known for its jazz (or maybe jazz-like is more descriptive) numbers. The movie still has some jazz, but there's a lot more rock, leading to a more fast-paced feel. The soundtrack is quite good without being overpowering and without losing the feel that "made" the series. The voice acting is as good as the series, which is not surprising.
At least two of the showings in the movie theater I saw it in were sold out. I imagine that won't continue, since this is a bit of a niche market and the movie hasn't been advertised at all that I've seen, but perhaps it will be enough to get a wider U.S. distribution for the movie, and Spirited Away picking up an Oscar shouldn't hurt either. It's worth seeing in the theaters, I think, assuming there's one near you. If you've ever wondered what sort of beating Spike can dish out when he's really upset at someone, this movie will answer that question. :)