A fascinating short game. Would love to see it made into a full game with a bit of a story behind it.
At first, I thought the stealth mechanic was there just to distract us, and that we'd be able to hack through enemies with ease, but the more I advanced, the clearer it became that a stealthy approach was the way to go. As long as you're fast enough, you can beat an enemy right after you enter their line of sight, but as soon as the enemies see you, your best bet is to run, because their firing rate and damage are too high for you to withstand.
This game has one of the coolest usages of stealth I've seen in a while in 2D games, and man, the bleak presentation with runic symbols and dark ambience puts me in the mood of something like Dark Souls, so maybe a really dark storyline would work well in a full game using this concept. Of course, you'd also need more features for such a full game, but that goes without saying.
If I were to criticize something, it's the fact that I completely forgot that the invisibility superpower existed and still managed to beat the game, so perhaps some more levels with harder challenges could remedy that.