What a polished game! And it's quite long too! Some puzzles had me stumped (parts of me because I was stupid with the second part of the code and because I didn't know you could swap objects between characters). I think I had the biggest problems with the code because I never knew which letters were already substituted and which needed changing. This confused me a bit.
The setting initially didn't click for me as I think I've seen enough underwater stations in videogames but the writing and interesting twists made it grow on me A LOT. I think some things came off as a bit flippant seeing that they just lost an "esteemed" colleague but overall the writing was really solid.