I assumed the end goal was always to have her reveal the secret of Miranda and how the crew was to deal with that. How long they dragged out the mystery of her trauma would have depended on how many seasons they had or what stories they had planned for the future. I don't think she changed from what she was planned to be, but she did adapt, we saw evidence of her terminator training in the series.
I would have liked to see how the characters adapted to the revelations in Serenity the movie. Granted, the comics compensate for that, and with some nice touches- Zoe's pregnancy and childbirth, the growing bond between Mel and Inara and Simon and Kaley, and the problematic large lump named Jayne. Sorry, I never particularly liked that character. And how is Zoe mourning Wash's death? How about the rest of the crew? What about River, who's now the strongest person onboard? What happens to her as she emerges from what happened to her on Miranda?
I haven’t gotten the comics yet, but I want to. I love River. She’s my absolute favorite. I would have hoped to see her grow more, and become a little more capable, but I wouldn’t want them to get rid of all her quirks! To me it was one of the best parts, her unpredictability, and sometimes her hilarious reactions to things. Plus, her constantly hiding up on the ceiling like a weird spider.