I friggin love this game!!! I've a lot of notes about it cus I'd love to see it evolve :3, I hope it's somewhat helpful!
I love the room design of every area. Of course more variety of rooms would be amazing but they're varied enough to frequently make wrong decisions and needing to dodge, which is good!
I also would love to see items fully resetting at the start of endless, and some rework of the shop. It feels busted, especially since you keep currency throughout all runs. Maybe instead, you could make the other items have a chance to spawn? (with a lower rate to the main 3 items of course) Or maybe reset your currency to 0 at the start of endless (and keep story/endless modes currency seperate?)
Aquatic area is unbalanced and too difficult imo (or too inconsistent for endless). The rooms last a long time, it's by far the hardest area to avoid damage, and it also seems to spawn very little items compared to every other area. Usually when you get hit in this area it feels unfair and unavoidable (walls of water enemies in a necessary corridor are very common), and it's an instant death effectively since the area is so long and you'll never find a syringe.
^ Also.. manta rays are flat-- so they're just a 1 pixel high instakill enemy that moves quickly & erratically. FINE XD but PLEASE make them more visible
Shadows in the Library area are too hard to see and can insta-wipe you when you enter a room. Maybe instead of an instakill you could do an "adadadada" struggle like the goo puddles in the warehouse!
Jumping feels bad, sometimes it doesn't register due to collisions and/or strafing at the same time.
It's already been beaten to death in the comments here, but it's true that items in the 1st phase of the Tigershark Fight NEED some regulation and should not be pure rng. Items (crowbars & syringes BOTH) can sometimes not show up for 5 minutes. The count of syringes is still often too high to the point where the only attack that actually matters is the waves. Look, I like it, but I don't need to sit through 13 real life minutes (I timed it) dodging the same easy attacks to get to the fun part. Artificially difficult, frustrating, and not fun!
The 2nd phase of the Tigershark Fight is awesome :) don't change it!!
(I have posted this to the form you linked as well)