Well, since you say in the end of the demo that the full version includes more things, I'm not sure as to what expect, but I'll tell you my impressions.
The game runs well, I had no problems with control, and it's nice to have a few color schemes to choose. I thought that the levels are too short and there isn't much variation in them. Also, I'm not sure if I enjoyed the character's penetrating bullet.
Now, my suggestions:
I think that you should come up with more sounds and effects for the enemies, the main character and the book shelves when they are hit.
I suggest that you make enemy waves a little more like they are in Space Invaders too, making them approach the bottom of the screen, you know?
Maybe you can come up with power-ups too. Instead of having the main character that powerful, she could get resources and shot types on the go.
*Of Space Invaders I have only played the Extreme one.