Hi, thanks for giving it a go and giving some good feedback! Overall it's meant to be bleak to match it's atmosphere. But I can understand it's perhaps too long.
Knowing how many threats there are can be helpful with managing ammo and your speed through the level. If there's only 3 enemies you can be less cautious and move quicker, handy for later when your oxygen begins to run out.
Melee is not supposed to be easy. If anything it's more of a deterrent and yes it can take a bunch of hits to kill one enemy.. the gun is your only sure fire way to kill them with one hit. It's more like the knife from resident evil... It's not much use but it can kill things.
The health bar shouldn't disappear when crafting so I will look into that, sounds like a bug. And I'm aware of enemies spawning behind boxes, but they really shouldn't around the exit so again I'll look into that too.
Monotony would probably be helped by reducing the levels by half or add more variety in enemies.