While Gaiman’s name is on it, I tend to agree with those who are asserting it doesn’t feel like a Gaiman book. It lacks a certain air of depth, whimsy, and morbidness that usually permeates his books (including those for younger readers.) I’m going to chalk this up to the co-writing.
Joey is a likeable enough character. He’s pretty bland and unremarkable, outside of the apparently stellar world-walking abilities he’s just discovered. He’s introduced as a heartsick high schooler whose primary interest in life seems to be his unrequited crush on a girl. The story then jumps into the preternatural before we can learn much about any other of his hopes, dreams, interests, or goals. We know he has a family he seems to have a good relationship with, but there’s very little interaction with them on-page.
There are times the inter-dimensional villains come off as a bit… well.. one-dimensional. >.> The plot itself is pretty formulaic: coming-of-age, worlds at stake, only our under-qualified protagonist can save the day… etc. Joey ends up attending a training camp for agents, most of whom are young alternate reality versions of himself. (Some of whom are VERY alternate.) And here I’d hoped to experience more of the culture and community seen in books that take a similar route. (Harry Potter, Percy Jackson, Hex Hall, etc.) But alas, not so much. Hopefully the later books may work their way into more of this aspect.
Don’t get me wrong--there’s plenty here to both satisfy and entertain a MG audience. I’d happily recommend it for them. But older readers and established Gaiman fans may want to “walk” into this particular literary dimension with some bracing knowledge.