The timid, pussy doctor turns out to be a psychopath.
And the douchebag who apparently left everyone to die comes back and saves the day.
Spoiler!
How is that even a twist? It had literally no effect on the plot line. Oh no, he's a psychopath. Had it been revealed he was working with the predators or something, or he in fact was a predator himself, or he was an Alien, or he was Ripley from Alien...yeah, that would have been a twist. It was just stupid.