Wow, this really blew me away and scared the crap out of me!
Spoilers:
Gameplay: Plenty of fun puzzles to be worked through, I really liked the valves in the cave, the hands, the statues and the paintings. Some of the chases and puzzles were pretty straightforward. I knew when there was a long hallway going to the middle of nowhere that I was in for it, some of the chases were basically a straight line, so once the initial scare wore off I was just holding down the sprint button and a direction key. The puzzle in the barrel control room could have used a little more work, rather than me just going "ahh, combination lock, the last code I saw". I only noticed a few minor collision glitches, the cliffs to the top right off the map in the first area can be stepped off, you can still collide with chemical B after you pick it up, you can wade into the overgrown pool out the front of the main elevator in the lab section.
Story: Lots of twists and turns in the story. I only got the car ending and ending D so far, I'll have to have another couple of cracks after the jam. The fear is kept constant throughout the game. My fear of the first monster (the metamorphised serial character of whom I've forgotten the number), wore off after my first chase, but it was soon replaced by a fear of Helga. I really enjoyed probing around in the laboratory, the feeling of "I really shouldn't be here" only grew throughout. The only criticism I really had of the story was I thought that it was a bit unnecessary that the events be a cycle (in ending D)
Presentation: Kept me on edge the whole time. The monsters and environment were just detailed enough to make your mind fill in the blanks. Great use of some very cool music.
Creativity: There were some really cool puzzles and monsters in here. This took me in a totally different direction than I was expecting, I kept expecting the game to be almost over but the rabbit hole just went deeper and deeper.
Horror: Scared the crap out of me!
Theme: I feel like this filled out the theme well, the story getting more and more unhinged the deeper I went into the earth. As for bonuses, I'd say that the underground labyrinthine laboratories count as a maze.
Conclusion: I'm amazed at how much you managed to pull off in the time of this jam. This was awesome!