In agreement with many of the other reviews on here, this was a potentially great concept for a film, unfortunately blighted by poor dialogue, unnecessarily exposition-dump-ey plotting, and some occasionally questionable acting (although I can't honestly tell if that just because the script was so weak).
The central sequence of the film; the underwater exploration of the titular 'deep house', was worth the watch. It all feels nicely SCP doomed exploration log-esque, and there was a lot to like about it - some genuinely spooky shots, really nice set design and cinematography, and just the right amount of 'no don't go down there'-eyness to it. But the sections of the film bookending the exploration, including the very silly ending, are really poor.
I really like that the filmmakers tried to do something interesting with 'The Deep House', and I think there's a better film hiding in there somewhere. I wonder if a production company like A24 had got their shiny golden mitts on it perhaps we might have seen a bit more fulfilled potential?
tl;dr - Pretty interesting, but inconsistently executed