I don't really know where to start with this - I've seen the directors YouTube series and quite a few other Backrooms videos (although I don't think it matters if you haven't and it's definitely a standalone film) and liked them, but I suspected the off-kilter creepiness might be spoilt a bit in a shiny full scale production.
It definitely wasn't IMO, and the atmosphere of tension and dread was all there in spades; anybody expecting a straightforward linear narrative probably won't enjoy it, but parts were genuinely like being trapped in a nightmare and I was with it all the way 😀
Definitely not for everyone but incredibly impressive for a twenty year old director. Great performances too and I think they actually built the set, which I never want to see in real life ever.