I played up to level 15 as I felt like I saw as much as the game had to offer.
This game is simple and fun but I can notice that past wave 8 you start experiencing lag when waves first spawn due to the amount of bullets. I didn't understand the book system as it seemed like the books only upgraded me during the wave and of that the red ones were the only ones that did anything. Maybe the blue books made me do more damage but I have no way to tell.
Having the player be forced to move around to get their "ammo" was a neat idea and took me a bit to realize how it actually functioned.
Overall a fun submission!