Criticism is criticism, and it's fair, no need to apologize. As it's said in the game's description, this is a proof of concept, not a finished product, but I'll address some of the points you made.
1. There is a tutorial that teaches all the mechanics of the player, but I agree that it teaches them rather poorly, that is, because the tutorial was an afterthought, as the game wasn't supposed to be public when we were making it, we decided after it was done to release it for fun.
2. Concerning both the health issue and enemy attack issue you brought up, the game is about being fast and precise, so one mistake and you're done, that is our core concept, repetition of the level until you get all the little things down and you go through it flawlessly in the end. But mechanics such as the shield enemy having to be wall jumped, the brass knuckles enemy being able to dodge bullets when shot from far away or the boss (who, fun fact, is called Sgt. Big Iron) having to be parried to be beaten, while they're were hinted at in the tutorial, again, it was in a rather poor fashion.
Anyways, thank you for your criticism and, most of all, thank you for playing and making a video about it, we're glad you enjoyed playing it, even if it was just a little bit.