Part of the problem with fitting the character development into allocated cinema time was that these characters were quite complex, so it must have made it hard to "version" them for the theatre - plus there were 9 good (sort of) guys on the ship, people they ran into and a villan, that's a lot of people to fit into that much time.
Its really the same problem they had with the TV series (I think), as the network it was on (Fox - and whos' favourite show will they cancel next?) wanted the whole world now, NOW NOW! And there was no time to introduce all the characters and let the world of the series unfold. Joss Whedon had a lot of success doing that kind of thing on his other TV shows, I can't imagine why Fox didn't allow him more freedom or give him credit for his level of expertise.
Anyways, its good to hear opinions of the film from people who were not familiar with Firefly, they matter a lot, perspective is important.
Its the world creation that's really got me hooked - everything is dirty. have been a bit sick of all those super-clean movies with SFX that is cool but meaningless.