As mentioned previously, Kaylee both endeared me and annoyed me. There were some definite plot contrivances. I won't go into them here, as I prefer not to spoil the plot too much, but some things were just too neat and too handy. Finally, it's obvious this wasn't a mega-money movie. You can tell from the sets and the paucity of big-deal special effects that Joss didn't have an endless bucket of money to draw from. Honestly, he handled that very well, so it's not a major negative.
In conclusion, compared to some of the trash that has issued forth from Hollywood this year, Serenity is a pleasure to watch. If you haven't seen it yet, I think it may be time to make a pilgrimage to the local theatre, especially if you're looking for a refreshing space western that breaks the Hollywood mold. As long as you don't walk in expecting the pinnacle of movie making, I think you'll walk away satisfied.