I actually thought the idea was quite good! The ending was a nice hit (hah! Get it? You get it.) and the voice acting was a wonderful touch.

Some things that could use improvement:

1. Some placement of things like the stack of books in the room with the lantern. The bottom shelf is unable to fully come out because they are in the way (to make this actually kind of a cool idea I recommend removing the stack and manually stacking individual non-static books).

2. A few clipping issues found, for example one above the doorway that leads out of the chamber.

3. The notes found could be formatted a bit better to help the flow. I felt the spacing and separation of sentences was a bit awkward though you could have just been going for that feel. There were also numerous typos (I recommend getting a proof-checker for notes in the future if English is by chance not your first language).

4. The maps reset upon entering them once more during the back-tracking segments. This means I was able to acquire extra oil and other pickup items my next run through.

5. Try to use some welders on the corners of walls to help tie them together - otherwise you can see abrupt wall ends and it can look a bit iffy.

6. The starting player area for each map is off the ground so when you spawn you fall a bit. Whereas there isn't anything wrong with this too much, it can take its toll on immersion. Just a quick lower on the Y-axes for the spawn area will solve that problem. :]

7. During the final chase scene the monster actually stopped chasing me almost immediately.

Though with that all said, I enjoyed the short story aspect of it all! Your use of monsters wasn't over-excessive which is nice, and even caught me off guard once or twice which can be a rare thing to do since I am so used to the game's atmosphere.

The build up of the castle madness was good, you didn't throw dead bodies at us right from the get go and waited until the chamber to show fully what kind of madness the doctors were up to. Though just as a personal preference and whatnot, I think a bit more subtleness in the earlier notes would have been made the story a bit more interesting. If the player already suspects the doctors were at foul-play then that can take away from the surprise! Though I found it didn't detract from the story too much which is nice.

The part that really hit home with me is the ending. I am a sucker for tragic endings and yours came with a good one. Right before he made it out he was smacked right down like the bug he is. Cue right into the credits aided by the wonderful work of Kevin Macleod and we have a good 'aw well sucks for him' feel while we mellow out from the music.

All in all, thank you for the time you put into this! I hope to see some more from you - I smell a lick of potential!