What I said up there. I gave this ten stars based on the extraordinarily original twist alone, even if the rest of the script up to that point wasn't particularly noteworthy and also acknowledging that the movie itself would've been a 5-6 for me if it wasn't for the ending.
See, I watch around 300 horror/thriller movies every year and I'm not particularly fond of twists, because I think they're done to death -pun intended-; around 90% of the time I see them coming from the get-go, even sometimes simply by reading the synopsis and picking some clues from the cover art or the trailers. I only truly appreciate twist endings if they're so genuinely original as to justify writing, filming and releasing a movie around them; otherwise, I honestly prefer clear-cut, straightforward narratives, as long as they're well produced and/or developed. Boring twists are boring, frankly, and sometimes even come across as a bit condescending and Dunning-Kruger-ish, specially when they come at the expense of the script's coherence. We see a lot of those, sadly.
So, that said, here we have this little movie: it presents a situation that genre audiences are overly familiar with -too familiar, even, which is never a good thing in my experience- takes that path and runs for the dots that connect it with, apparently -and deceitfully-, little appreciation for imagination or originality. It's competently shoot, acted and cut by reliable professionals obviously used to make the most out of meager budgets, so I think 'meh, but entertaining, so I'll stick with it and follow it to its inevitable 'the apparent good guys are actually the bad guys and the apparent bad guy is really a grief-striken father/husband/brother/whatever getting his due revenge' or 'they're actually dead, the derelict hospital is Hell and the mad doctor is a devilish entity making them pay for their sins' ending and move along. Then, the ending rolls out and I suddenly realize that I've been actually watching one of the most original subversions of a classic literary work of fantasy horror I've ever seen in my long movie-watching life. What can I do after that but saying 'well played!', nodding with a complicit smile and give it that 10 star rating to overcompensate for the low ratings left by every genius out there who thought the ending was stupid, when the opposite is true?
It has a soul, if nothing else, and that soul is firmly planted on a soil made not of the dust of the overdone torture * subgenre, as it may seem at first, but of that of old Universal and Hammer classics from a glorious past. So, ten it is, for me at least - won't blame you if it isn't so for you.