This film was really disappointing. River Tam, who felt like the least developed character in the television show, unexpectedly became the central figure here. Even though she’s described as being slight and inactive, River managed to fight and knock out everyone in a bar. The team inexplicably made it their mission to travel to the planet River wanted to go to so that she could learn about her history, despite having previously displayed anything from dislike to outright calls for her death. The antagonists are baffling. They’re portrayed as being so savage they raid planets and eat people, but somehow still coordinate well enough to operate spacecraft. These supposedly feral individuals all originated from the same planet River is trying to reach and a research center. It's suggested that around 1,000 researchers and support staff were initially affected. They have no means of spreading their condition because the facility was closed down, but now there are far more of them than originally existed. The explanation for this is unclear. The storyline doesn’t hold together; it isn’t captivating. None of the personalities are compelling, and when characters die, it doesn't affect you. Skip this movie. Like the TV series, it’s a pointless use of your time.

Source on TMDB