Very creepy, really quite scary, and has the potentional to be very triggery, but very, very good.
As a warning for the level of triggeryness: the opening scene is three children being forced to commit suicide. This is the recurring theme of the film.
And I think I did watch a good third of it with my eyes either shut or focused firmly on my lap.
Interestingly, the ending is quite different to the play, and is marginally happier. I think. Sort of. Depends on your definition of happier. Certainly the lead ends up more content than he does in the play. (I’m doing my best not to spoil it).