I voted "A bit scary, but mostly annoying."
SPOILERS FOR THOSE LOOKING FOR INFORMATION ON MONSTER BEHAVIOR IN THIS GAME AND HAVEN'T PLAYED IT YET!!!
So I think the encounters kind a got interesting from time to time, but the one that was most interesting to me broke in a spectacular way.
In the Theta labs the monster was pretty scary. I still have no idea how it behaves, does it go for sound, sight, movement, protagonist breathing or something? So I got to the recording that's in the medical room with surgery equipment. As I was listening to it, the monster came in the room as if to check what the sound was. I was next to the recorder and turned my back to the monster constantly so it doesn't detect me. So I was like "Sound! It attracts to sound! I'm gonna trap it!" So I tried making noise in various rooms, but I think it despawns so it's really hard to say if it even heard the glasses I tossed around.
We skip a lot of time me getting killed few times when I was in light and I think it heard me at one point.
But the one that broke it for me was this: I was in the dark corridors. Just trying to sneak by and stuff and he heard me, I started running from him and then he hit me once. So I was like "F this, let him finish me, I don't want to play this level 'hurt'." And I stood there waiting for the second finisher blow, but it didn't come. He just forgot about me and started treadling around again. That really broke it for me.
Also I didn't really like the ones you had to not look at. Seems annoying.
But overall it's an amazing game. That ending still comes to my mind occasionally. Great stuff and can't wait to see what kind of "super secret" stuff you guys are working on!