I'm of two minds on this one. It's an average mystery with a crazy premise. In that regard, it is just like the first novel. The main difference was that this one was rather full of extremely light philosophy disguised as deep revelation. 
 Being a short novel, I'd expect a long list of throwaway characters for the detective to explore and discard, but those were rather light. What we do get is a long list of imaginary friends who make his life interesting, almost overwhelming the actual mystery. 
 If the mystery had been stronger, or at least as interesting as his complications, then I might have given this four stars. Perhaps I would like this series a lot more if Mr. Sanderson comes out with dozens of these to built a really significant corpus... but I'll be honest with you: I'd much rather see him continue his epic fantasy series or even a few of the other YA series. If he could live forever and pump out books as quickly as he has been, then I doubt I'd ever have this complaint. 
 Otherwise, the premise here is a little gimmicky and the psychology is a little lax. It doesn't ruin the read, because, after all, we need conflict and pacing, and Mr. Sanderson doesn't let the novel slide. 
 It wasn't bad, but it wasn't my favourite.