It’s an imaginative series and I watched 5 of the episodes but didn’t make it all the way through episode 6.
I think the two main things that make it unbearably unsettling for me is its slow pace and quiet soundtrack. Firth makes you wait and wait for a horrible thing to happen and he makes you think what it might be. By the time it does happen, I have imagined a bunch of nastiness.
The monologue is great too. “You smell like soot and poo.” “Don’t you like my mouth-words?”