Not as good as I'd hoped

Great performance from Pattinson, and possibly a career-best from Da Foe. Beautiful cinematography. Fantastic location. Superb visual FX (I loved that shot of the mermaid swimming underwater towards Pattinson). But that's it. It didn't grip me. Two guys go stir-crazy. Or maybe not. I've seen it variously described as a horror film, a thriller, and a character study. That last one I can see. But as for the others, at times it seemed to border on horror but never quite went over the edge. And it never thrilled me. I saw a theory from a poster on here that viewed it as a fever-dream of Pattinson's character, as he's being eaten alive by seagulls after being shipwrecked; there never was a lighthouse (there isn't one in that final shot), and there never was a Da Foe. I find that idea more interesting than anything I got whilst watching it. The pluses I mentioned get this a 6.5/10. But that's it.