I really like how you took the theme of confinement in this game and didn't make it a generic horror game with a monster at its centre. Psychological horror is a lot of fun, and through having multiple endings and room for exploration the player gets to learn slowly about the broader narrative. 

The writing on this is very solid. The internal monologue of the protagonist is written well; it's relatable but not melodramatic. There's lots of description dialog for items which helps build context to the story, and the ending narrations do a fairly good job of tying the broader story together.

The level design is quite nice too. The assets you've placed ingame really combine well to give off a post-apocalyptic bunker vibe. There is some good atmospheric turns in here, such as the experience of crawling through vents and discovering the body, that definitely kept me well on my toes. 

Some constructive feedback: 

• As others have said, the assets are slightly all over the place in terms of their fidelity. If you're looking for ways to explore better visual consistency, try downscaling textures, or adding a screen filter to get the right effect. 
• Signalling is a term I like to use when you'd like the player to figure out or recognise something.  I think there were some good attempts at signalling to the player the mysteries behind the game - the sound effects in the vent and the note at the end. However, some of these clues could have been a little more helpful to guide a particularly observant player to the good ending without having to finish the game and restart. Or maybe I missed something, in which case...completely disregard this! 

I did a playthrough below: 

Thanks for submitting this to the jam! For a first game, this is a great achievement.