Powerful stuff. Had me hooked beginning to end. I, too, found it oddly (extremely?) relaxing, especially some of the stuff about itchy hands. It felt deeply personal, yet also distant. I really liked it, but I have some suggestions.
The traditional FPS style controller doesn't suit the visuals well in my opinion. Every long corridor I got to, I'd look at the end and take my hand off the mouse because too much vertical movement gave me a headache. I think something like traditional doom controls (up/down movement & L/R rotation) would suit it more appropriately. It's nice too look around but the vertical camera movement almost seems unnecessary the way scenes are rendered. Vertical camera movement also gave me a bit of a bug on the river where the red texture disappeared/reappeared at different angles.
Subtitles would be such a welcome addition. I found myself almost dissociating from the game to listen to the narration to make sure I clearly heard every word. The voice acting is so well done, as is the other audio here, but when the music and atmospheric sfx are going with VO, I start lending less and less attention to the VO.
Great work for a one man expedition. I only say so much about the negatives I saw because I like what you've done so much.