It's not a book, it's a webcomic. Although not like any other webcomic you've probably seen. Its format is kinda parodying choose-your-own-adventure stories.
The beginning is random because the commands were all reader suggestions. Then the readers gradually got less control over the story, and it got better. I really like all the time loops going on.
Be warned though; It's rather filled with swearing. But don't let that stop you, it didn't stop me. Just don't mention that to your parents.
Also, that wiki is filled with spoilers, so I think it's recommended to catch up with the story first, no matter how long it is. Part of the fun, I think, is to figure out the things by ourselves and maybe coming up with our own theories. Then again, I'm kind of a nerd.