Alright, then I'll start with the things that stand out most:
>First of all, the slippery movements. It was very difficult for me to land some of the smaller platforms, I also noticed the skidding would occur even if I was dropping straight down. Good, satisfying movements are essential especially for these kind of games! If you want a little bit of skidding, you could probably get away with it, but you also don’t want the player to feel like they can’t control their movements. ;)
>Limited ammo. I know you have the warnings up, but the player should have at least one attack they can use without limit; you should also make sure the player can’t softlock themself, which I fear would happen if I exhausted my laser and therefore couldn’t open any of the doors.
>Finally, the keyboard layout. The keys you chose for jumping and movement are alright, but the attack keys should be done with the opposite hand. Let me elaborate on this a little further:
If you’re using WASD for the movements, it would be more intuitive to place the attack keys somewhere on the other end of the keyboard, like U, I, O, and/or P, or any of the letters from the lower respective rows; that way the player can use their left hand to move, and their right hand to attack. The same logic applies if you use arrows for movement, make sure there’s a setup where one can comfortably move with their right hand, and attack with their left. (I hope I’m making sense. XD)
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Those are the 3 big things I would consider revising going forward. Now, some of the smaller details that I feel could improve the experience:
>Have the enemies react when you shoot them. Have them flash, make a sound, maybe even push them back a little bit (That last one is optional). Have something in place to let the player know their attack is working!
>I feel like the acid pit in the cave to the right side of the map should just be an instant death, or at least deplete your health at a far quicker pace. Unless there was a way for me to get out (That I wasn’t finding), I was left just sitting there, waiting for my death to come.
>I tried exploring the left portions of the map, passed through this abandoned base/shelter, and when I came out I started falling into an abyss. And I just, kept falling, there was no end to it; no death or anything.
>I noticed someone pointed out having a windowed mode option, and I agree that it would be nice to have that. Truth be told I usually prefer playing windowed mode. There also didn't seem to be an option to exit the game? I resorted to using ctrl+alt+delete to open the task manager and force close the game.
>This last one’s a very subjective opinion and maybe it doesn’t bother anyone else, but I wish I could turn the voice volume off; I find the main character’s shouts kind of annoying. :/
By the way... Is that Metroid music I hear, or rather a remix of it? I’m no copyright expert, but ya might wanna consider swapping that out for some other tracks. If you need music but can’t compose/don’t have a composer, I’d suggest giving https://opengameart.org/ a look! There’s a bunch of free assets that content creators will upload there, including graphics, sounds, and music. Just make sure to investigate the license for each asset, and check to see if their respective creator would like to be credited. :)
I hope this wasn't too overwhelming for ya; I've been doing gamedev for almost 15 years myself; you know, I was actually somewhere around your age when I was getting into it. XD
I'm wishing you the best going forward! :D