Your game has a great visual identity; everything blends well together and is easily visible against the background. The game has great player feedback as the player's health and enemies left are always shown on screen, and the direction of both the ship's movement and where the player is aiming is clear to the player. I especially like the arrow pointing the player towards the boss/portal in each level.
I only have two real criticisms for this game. First, the movement of the player's ship and enemy ships is extremely slow and sluggish. It is still fun to shoot at enemies and dodge their bullets, but the act of moving around can be tiring due to how slow the player moves. Secondly, I would recommend adjusting the damage values of the enemy's bullets. I noticed that the enemy bullets only deal 1% of damage, but colliding with an enemy deals 25%. I think that the damage values could use some adjustment to lead to a better difficulty curve.
Overall, I think this game is well designed with only a few problems holding it back. Well done!