I think that has to be the first suspenseful movie I've watched without getting a nightmare; and although I did jump a bit when the moment was dark and they were being ambushed... I rather liked the ending ;D
It took me awhile to figure out this movie's name, I could only remember that it was a quarantining-a-illness-related movie with a group of people being 'naturally' immune to it. Reminds me of the phrase, natural selection.