This movie is similar to the The Sixth Sense, in that it takes a difficult subject and presents it well.
The acting was excellent. The story was excellent. The director did an excellent job in presenting the story. It kept you on your edge ... both thanks to the special effects, as well as keeping you wondering what it was all about, and how it was going to end. And it did all this without becoming too confusing or overly complicated. In other words, the plot flowed very well.
One of the best parts of the movie is how well it brings into relationship two points of view: reality, such as we know it day-to-day vs. the unknown.
The story is complete from the start to the end. Then ending leaves you with a sense of completion.