The premise for this does not prepare you at all for what is to come, but perhaps the initial quote by H.P.Lovecraft will. On the surface, it's two escaped survivors of a Heaven's Gate-like cult, getting a videotape message and going back to the commune and finding old friends.
Then they see things in the sky and the water, and beyond the totem poles. Then they receive more messages. Then the truth of everything is revealed.
This is maybe the best strange tale I've ever seen as a movie.
The older brother's acting is wooden and fixed in a permanent blank stare and smirk, the younger one's a little better, the other characters are either stoic or insane, or underacting or overacting, but it's the story that drives this.
I don't like the final scene, there's too much closure and that's not what this story's about.
But you must absolutely watch this.