The parallax effect is pretty sweet. The controls are pretty responsive and they aren't sluggish at all. This is pretty for your first game in Godot! I hope you have a fun time learning more about the engine(even if you don't stick with it!)
One thing is the sound effects of the enemies dying are pretty loud in comparison to the normal shot, so when you're killing a lot of them in a moment, it's actually pretty harsh on sensitive ears. The enemies are also cute, but they are pretty similar looking, so maybe some variety would be nice, in both the style and the behaviors.
Good job on implementing this side scroller!