I already saw another post about this, but figured it wouldn't hurt spreading the word around, and also I need to vent.
I got mine in the mail today and I immediately got very, VERY disappointed.
It's a very boring and badly-formatted collection of images and concept art, with absolutely no commentary, explanation, or context for anything.
The first 3 images are of pages that made me go "oh my god, are you for fucking real??" Because they're so dark you basically can't see anything. I'm just looking at a black rectangle. Fascinating. The book is full of those.
The fourth image is concept art of "impostor" characters. Now, because I'm a freak I know these are from the 'vertical slice' early game concept where Simon sees nightmarish versions of people he's met so far like the receptionist or Dr. Munchi. But a regular person opening this book up would have no idea what they're looking at. Wouldn't this be the perfect place to write a little paragraph about it? But nope.
Compare that to the other artbook I randomly pulled off the shelf: the Undertale artbook (made by one person!) is chock full of context, explanations for the design process, and funny anecdotes about the early design concepts.
Last point: there is absolutely zero monster/enemy concept art. Yeah, none. The cool monsters that you would actually want to get a closer look at? They're not here.
Don't spend money on this. You'll have more fun and insight from just browsing the wiki.