Extremely underrated!
I just saw it and in my opinion it's almost great. Amazing performance, some awesome shots; the suspense is slow at the beginning, but dynamic at the end... Some quite good scary moments. Excellent direction.
The monkey doesn't look evil or ugly or something. It's somewhat cute, that's why it's in fact eerie.
My rating: at least 8/10, maybe even 9.
I also liked the association with "Misery".