Dear Frictional (some advice)

[humanoid]

But he can open doors. I hid inside one of the rooms and he opened the door, wandered around, and then left. He doesn't just teleport.

OP was talking about the fact that you could lock (not just close) certain rooms in this particular area and with a bit of effort, trap the monster inside.

I actually did the exact same thing the first time I played through (didn't take an hour to do that though) and yes I was also somewhat disappointed to find out that he wouldn't stay in there forever (he did for a few minutes though).

However I did notice beforehand the vents in the area (including this particular room) and the fact that there was something crawling around in the vents 1) before the monster of that area first appears and 2) when it was "unleashed" but not near you, so yeah I went with that explanation.

And even if there weren't hints/"excuses" like that I wouldn't get butthurt over it and call it an "unfinished disappointment", in fact this is a more polished game than quite a lot of "AAA" games out there.

But suit yourself, its your loss of an otherwise outstanding game/story experience (just like that other person that posted here who wouldn't accept the choices presented to him, I guess some people are really that nitpicky).