This book is by A. Lee Martinez.
Do I really need to say more? It's his fifth book and third foray into the fantasy realm (realm being relative, the whole book takes place in one building), it does a lot of interesting things while being readable (I know! I read it!), humorous (though his continuing trend of replacing humorous with entertaining continues, and is awesome), and human (despite not having any humans in it beyond the first chapter or so).
So I'm not going to say any more, if you need to know more about Martinez go read the other four reviews. I will say this though: his blog looks interesting and he ranted about how other authors look down on him because he's not writing a series. I hope he never starts, he's far too good at creating fascinating one-shot worlds.
Also, it sounds like 3 of his books have been optioned, one attached to David Fincher, which is pretty awesome :)