So many particles! xD I liked it ^^ It was fun ^^ I have a few comment:

In this type of shooter, you should add the option to just keep prressed left-click to continuously shoot. It can be tireing to spam click and will discouraged player.

 The base to protect isn't clearly presented as something that needs protection. At first I thought it was a shape like the others and tried to shoot it.

I like the art style. Although simple, it's a very beautiful game.