I had a lot of fun playing the game, here's some personal feedback but keep in mind this is just my personal opinion.
* It would be nice if there was a way to see what upgrades you have and what they do.
* Moving back and forth between bookshelves isn't too bad but I'm wondering if it'll start to get tedious once there's 1M books. Being able to move back and forth with WASD would at least be nice.
Still, I would love to see where this game goes, its a really satisfying game!