Reading the scene-by-scene breakdown confirms my reaction when I first read the script, then saw the movie: The story’s three acts can be seen to play out like this:

Act One: Drama.
Act Two: Thriller
Act Three: Horror

The thing is, it doesn’t feel disjunctive at all, rather it flows one movement into the next and builds in scope, tension, spectacle, and ultimately meaning. And what a fantastic reveal in that last shot!