I saw it twice. I had to, because I was overly critical the first time, since I had red both the novelization and the screenplay, so I spent the first time looking for sceens that they cut. The second time was pure enjoyment.
Just a few points and complaints-
The scene at Miranda, where the camera spins around and around- the only shot in the movie I didn't like. I almost hate to put it this way, but it almost made me...dizzy.
The only other thing I really hated was when they went from a very dark shot to a very brigth shot- it hurt the eyes.
Other than that, I was sorry that some characters didn't get any screntime- characters like Wash and Book (and Inara), though I understood why they couldn't fit them in more.
I remember listening to the commentary track on the pilot for Firefly, when Joss decribed his idea that the Alliance vessels would be verticle, like skyscrapers. I was never a big fan of that, but it's too bad they scraped that idea.
Other than that, it was a great movie. I went with a friend who never saw Firefly, and he said afterwards he'd probably try it out.