Hey, nice to see another gamemaker game! I wasn't able to finish it, the difficulty was a bit punishing (the timing on those flamethrower tiles got me) but I got a nice look at it I think. No damage for the yellow bar in combat seems pretty harsh, and in general the pointer on the bar feels like it moves just a bit too fast.
I wonder if you use emulators often, as the control scheme reminds me a lot of the good old days. I don't encounter ZX for keybinding often, and a WASD alternative would have been welcome, but it didn't take me that long to fall back into the old bicycle seat, or however that saying goes, haha.
I am wondering what is the game design choice between having to use keys on doors, but just walking into a wall switch to trigger it. My suggestion would be to automatically open a door when walking into it while in possession of the necessary keys.
The presentation is well put together, and the movement itself feels good! I feel like you've got the bones of something solid here, it just needs some polish.