I picked this up randomly, have not read Dee's other books, nor was I aware of the hype surrounding him as the 'next Great American author'. In a way, this was good, because I was able to just read the book, without any expectations at all. And for me, it was fantastic, one of the best things I've read in awhile.
It is conceptual in the sense that it encompasses so many themes - contemporary art, the line (or lack of one) between advertising and art, perspective, religion, the subcultures of America, parent/child relationships, sex and subversion, intimacy and more. These themes are represented through both the form and content of the book, and even the characters. This may have been why some reviewers found the characters non-compelling, or the changes in perspective from section to section distracting. Personally, I felt they were brilliant, each laying open another layer to a theme that wouldn't have surfaced otherwise. I feel this book is like a prism - you keep viewing the themes and the story from different angles, first looking through one side of the prism, then another.
From a purely psychological perspective, the ending is not very satisfying - the two main characters don't get together, and no one really gets to ride off into the sunset. But I don't think it could have ended any other way. It's true that the slogans/quotes used in the final section are hard to follow (as one reviewer stated), but they make their point if you spend some time with them, and the whole last section is a natural evolution from the prior two.
I think what really makes this book a worthy read is that it is able to cover so much conceptual territory while still keeping you engaged in the story. I wanted to know what was going to happen next, and I don't think there are that many novels taking on these themes that manage that. So read, think, and be amazed!