Honestly quite fun but it has some small issues.
Starting positive, i like your character sprites, they have quite some cool little animation for the low res style you went for, and i like the very John Mcclane inspired player character (at least that's the vibe i got from him XD)
The controls felt nice and responsive and i like that you have a reload mechanic in there, on the plus side your game works with a controller, not sure if you planned to have it since the in game prompt only mention keyboard keys, so it's a cool bonus ^^
Unfortunately there are some issues as i mentioned,
combat is really hard cause you can only shoot straight foward and your level design has slopes, so this creates some situations where you can't really attack enemies unless you jump right down in the middle of sometimes groups.
Some of the jumps are a bit hard to judge like the one after you collect the yellow keycard.
And finally it's too bad there is no sound at all in the game, i think with some sfx and a small music loop you can add quite a bit more life to the game.
Now with that said what's good here is really good, and i had a good time trying it, i don't know if it was one of your inspirations but your game to me really has that oldschool Apogee platformers vibe like the first Duke Nukem for Dos.
Keep up the good work, good job :)