The novel is not the basis of the anime. It's like an "alternative ending" that was written after the anime. So watch the anime before reading the book!
This book was written with three rules to follow.
First law: Keep the appeal of the original story intact
Second law: Compliment the original story with a new perspective
Third law: Include a new episode unique to the light novel
Story: As a HUGE fan of the anime, I can honestly say that the novel is not only really good, but also a perfect source if you want more of all those interesting characters. Now, it is like the anime in
the beginning, but then it branches of into it's own unique ending, while keeping the appeal of the original story.
Art: The pictures are in the same style as the anime. But if you're a perfectionist you might notice some weird mouth shapes, or dislike the dark contrast. But I honestly think it's fitting for the atmosphere of the story.
Overall: There is no real complaints about the book. It's a perfect side story for the fans out there. The ending was more of a personal finish for the main character, rather than the anime ending which focused a bit more on the best friend and the cafe owner.