Geez that film is unnerving. Not exactly terrifying, but deeply, deeply unsettling.
And Florence Pugh is both gorgeous and an amazing actress. That is a helluva performance. I was already kind of a fan, but this is other-level stuff.
I will say that I sort of saw the ending coming early on, so I wasn't shocked at the film's last moment. But even if you guess the ending, the journey is SO disturbing...
If you thought it was slow and boring, I'm not going to argue with you. But if it had been "faster" it would have been bad, IMO.
The contrast between the parts that are very naturalistic and the drug trip scenes also makes the film disturbing. A scene can seem very naturalistic and spin into drippiness.