The filming is gorgeous and the chemistry between the two main actors is brilliant. While the story takes a bit to form, the overtones of Lovecraft and the descent into madness, or utter reality is riveting.
What's real and what's imagined makes the viewers point of view, the third person in the Lighthouse. Are we being "gaslit"? Are we too falling prey to madness? Is some of this real? Where's the line we walk?