I didn't like it. I mean, maybe I just didn't understand the idea, but this book was a little bit annoying to read. I always feel uncomfortable to write a negative review, but I can't avoid it.
0. The style. At the beginning it was pretty much like actions-describing people-actions-who did what, who said that... boring...
1. I don't know why this guy decided not to leave his room, obviously he has some sort of mental disorder, but I'm quite confused, because the reasons are unclear.
2. Why his parents and his sister are so stupid? Ok, your son is acting weird, he stays at his room all the time, not even speaking to you normally, would you be even curious why? Here we have parents who simply don't care and even stimulate his strange lifestyle! Firstly they say "ok, we let him go through this on his own" and then they decided to act like he doesn't exist! I mean, how will he recover if they don't even try to help! It seems like they have more than enough money for therapist or like some sort of medicine, but no, they didn't even think about it!
3. The Hikikomori thing was mentioned ONCE in a whole book.
4. Till's strange actions and descriptions of his "world" were strange, but it was the only interesting part of this book.
5. The ending. OH PLEASE, why can't we still have the ending where everything will be explained?
To sum up, I liked the idea and some parts were actually good, but not to offend the author, but I think he hadn't studied the concept of Hikikomori as much as it was needed for the book. It wasn't explained for the reader, that's why I was so confused.
I'd recommend you "Highly Illogical Behavior" where almost the same things presented just better and in a more interesting way.