--I mean, atmosphere sounds like a main character?

I think it is. Certainly the sea is. It's one of the movies that looks like a good prose style.

I took a look at the trailer and liked the sideways-reaching lightning. And there's a shot of the light of the lighthouse near the end of the trailer that looks worthy of the words you quote from the senior Tom.

I just rewatched the trailer—I hadn't seen it since the summer before the movie came out! It is in some ways an accurate representation of the film and in others actually undersells the weirdness, but it made me think of the effectiveness of the siren's song, because in general I hate trailers and I remember hearing A. L. Lloyd on the soundtrack of this one and seeing the glimpse of the mermaid and thinking I felt extremely pandered to.