Well, there is development. Over the short course of the series, Simon became more accustomed to his life "in the black." His wardrobe got more relaxed. He fought off an assassin. And there's all that time in between. I found it really cool that Simon was punching Mal in the movie, when, in the episide Serenity, it was the other way around. It was like they had come full circle.

The biggest thing that annoys me about Serenity is the time issue. In the movie, Mal had said that it had been eight months since they took in Simon and River (and Book). And, correct me if I'm wrong, but I'd always heard that the movie takes place six months after the end of the series. And that would mean that those 14 episodes all took place in the span of two months. While it seems unlikely that the development of the characters could have happened in that span of time, not to mention all those different situations, it kinda cheapens it to me to think that they had such little time together. And, also, in Trash, Mal tells Monty that the events in Our Mrs. Reynolds took place half a year prior to then. So I'm confused.