I read some reviews of this movie that said that it moves too quickly for you to feel anything for the characters. I think that speed of storytelling dumps you right there on the beach with the characters of the story, and gives you a compressed amount of time in which to work out what is going on as well.
Once you work out that they are aging, which happens pretty quickly, then you are on the hunt for the twist. It’s not an M. Night Shymalan movie without a twist, is it? And you know that it starts in that moment when you become aware that the occupants are being watched.
I think the twist is interesting, and it really does make you unsure whether to take the villains of the piece as straight-up villains. Intention versus method and the inhumane method of obtaining their results is the thing you have to square. But if there were to be a sequel then the question becomes what could this place be in the hands of those to whom it is delivered.
I think the acting is fine. It is exaggerated in places, but with this kind of movie a somewhat hysterical slant on that seems fitting. The aging process is handled pretty well. If I were to place it in the rankings of Shymalan’s films I would consider it to be a solid effort, but not one of his best. Definitely very watchable though.