I think people are disappointed because the build up made it seem like the finale was leading to something deeper and more grounded psychologically. The hands didn’t feel like they were meant to be literal hands, but symbols for something more complex. Same with the mirrors, a lot of people expected them to explore the psychology of genuinely sociopathic characters or themes of identity, self perception, repression, something along those lines.
Instead it all turned into straightforward paranormal stuff without much deeper meaning beyond “there’s malice inside everyone and embracing it sets you free". That’s what made the ending feel unsatisfying to a lot of readers. The story kept hinting at depth that never really paid off.
I remember reading this a year or two ago and I really really liked it (still proly in my top 3 faves) and I went to check the reviews out of curiosity and apparently everyone thinks it's mid???????? Guys just because the ending was supernatural doesn't mean the story itself is mid T_T