I'm not at all sure what to make of this one.
Is it philosophy? It examines the meaning of life through the study or our simple, daily activities and thoughts, so perhaps.
Is it humor? It clearly points out some of the oddities of human nature in ways that make the reader laugh, or at least crack a smile.
Is it satire? Certainly some bits - like the long footnote about footnotes - can be thought of that way.
Is it meditation? Nothing "of the world" discussed here is particularly important, and yet, something about the presentation makes the whole something greater than the sum of its parts.
Is it some kind of high art? Well, maybe, but I'm not sure I could defend that description.
In my opinion, The Mezzanine is a novel written in the style of Jerry Seinfeld, only extended. Seinfeld's comedy has been described to me as being "about nothing", or at least about nothing important.
The Mezzanine - in which the entire plot revolves around the author's thinking over one escalator ride, with extensive diversions into things related to those thoughts - is Seinfeld's comedy on steroids.
Instead of a few lines about broken shoe laces, we get whole pages with footnotes and later references. We get an interesting discussion of the frequency of the author's thoughts about various topics, and the idea of comparing that data with similar charts for others. We get expositions on cashier efficiency and polishing the handrails of escalators. In all, it's a disordered and unrelated group of chapters, very loosely bound together by the author's occasional reference to his return from lunch.
But in the process of writing these un- (or barely) related blurbs we actually examine the way people think. There is amusement, at a minimum, in these pages as a result.
In all honesty I don't know that I learned from The Mezzanine. I already assumed that everyone had crazy thought patterns similar to my own, but different in their specifics. Still, I did enjoy it. Recommended.