I've read Level Up! cover to cover and can vouch on it being a pretty good book on the subject. The guy gives good lessons & examples and the book doesn't feel like I'm reading a textbook or something. I recommend it. A Theory of Fun is another good resource. Helps you think high level on what you are trying to bring to the table here.
That said, a good number of these books are about tabletop but I feel like the ideas there could translate well. I say this because I got the idea for the game I'm currently working from a board game. I've heard good things about the Kobold guides but haven't checked any out yet. To be honest, I plan on picking it up specifically for the kobold guides and the puzzle guides. I'm weak on puzzles and I'd like to make something Lufia-esque some day

thanks for the heads up,
@Andar !