Interpretation

Midway through I thought maybe it's a purgatory/hell story. The light is heaven. Not totally sure though, but I think Pattinson is about to become a seagull.

The island is Robert's purgatory, his punishment for letting the real Winslow die. The light represents heaven/redemption.

I don't think anything that was happening was real. The end clearly ties to the Promethean myth, as Prometheus was punished by having his liver eaten by birds every day, and obvious parallels with the light and the stolen flame. It also looked like Willam was playing Zeus a few times, especially when shooting the beams out of his eyes. Except this was more Proteus. I honestly don't know what to make of the film, but it was seeded with oodles of symbolism. Whole damn movie might have just been a spin on fables and mythology. I really think it was just an arty director having a blast mashing up some myths with a slick Lovecraft inspired veneer. I'm not sure it's any deeper than that.

I think it was Pattison’s lingering guilt and frustration building up on the island, combined with the fact that Dafoe was also a looney that didn’t make the situation any better.