Well, i have some things to point out which hopefully help with properly fixing up or improving some things, some you may already know, but just mentioning it just in case:
1- Has the 'Death by Pressing D' Hotkey or debug always been there? This could be part of the current devbuild or something but i'd suggest putting those hotkeys for the F Keys to prevent accidental input (Like F1, F2, F3, ETC.) and if not to the keypad numbers at least, i know this is work in progress but that alone should be away from the main controls at least for the public build because it makes it feel more that it is unfinished which i know it is but still
2- This one is obvious but I'll mention it anyway: some objects in the level don't align with the background as I am walking over what are meant to be supports of something above Grant and such, which can feel off
3- Oddities with the stairs: Using it works well and smooth enough, i think but upon reaching or getting off it is weird, reaching the top it can cause some accidental bouncing instead of just having a transition animation to reaching the platform and not being able to interact with the stairs unless i press down on it again, sorta same goes with finishing going down
4- Not everything has to be THAT authentic: Unfortunately things such as moving the camera down by just ducking needs to be tone down a ton or straight up removed, same goes for the fall damage, if for authenticity sake you can have a toggle to make it feel like the original exactly in terms of difficulty just like 'Faces of Evil & Wand of Gamelon Remastered' among other things
Other than that, you are achieving the authentic feel, some of the game felt off in the original due to the limitations of the console (or probably not well optimized back then) in which some cases there was lag but obviously on modern day with no limitations, it felt entirely smooth. The same goes for the controls and since it's just the 3 buttons makes it a lot easier to work with
I wonder how you'll handle his weapons, since often the biggest weird thing in the original is just how reliable and most effective and consistent of them all is his regular tranquilizer gun, if you add more weapons i hope you give it a nice way to switch between weapons since cycling with oen button is not as ideal as it is to cycle left and right with pressing a 'L' or 'R' button of sorts
On a side note: I've seen you on a video somewhere in which someone remade some gameplay of the original using WAN, which looks impressive, if you tend to have that kind of aesthetic, i am hoping by the time you finish the base games first you have a toggle to switch in between the original and remade graphics if you do. Same goes if you wanna remake the music or get someone to compose it though i am getting ahead of myself there.
This sure is an ambitious project of which i am hoping you keep progressing through it because it can turn out to be something real big