It's not really a metroidvania. You just go through a level, kill enemies and occasionally get a upgrade for combat.
The level design isn't that inspired and there is no theming.
But I like how the game controls. The jump feels nice and the shooting is decent. The best thing about this game by far is the blending effect between enemies or the player and the environment. No idea how you did that.
For the combat design:
If you only care for reaching the end, the shield is by far the best option. The fact that you can move while shielding and the regenerating health make the game way too easy. Maybe you could decrease the movement speed when using the shield of disable the jump.
The regenerating health in general isn't that good of a design decision. It promotes a playstyle where you go in guns blazing and then sit in a corner, far away from the enemies and just wait. It would have been far more interesting to have health pickups or some other way to gain back health.
Despite all my issues this was still an entertaining little game. Congrats for finishing it.