Very fun little game! Love the art style you went with the nice fps controls.
Some constructive critique:
Level 1 - Its not very clear what objects the player is supposed to collect and how many. Some sort of tracker or indicator would be helpful.
Level 2 & 3 - I like the addition of the healthbar for the enemies but I would personally have it always rotated to the players perspective (it currently rotates with the enemy). Also the projectiles seem to deactivate early sometimes when pressing the fire button quickly. Could be related to the object pool (if used).