My first reaction was that the narration is growing up, and it is, but my second reaction is how much more enjoyable the read is. Sure, the cultural references are simply a nod to the readers showing us what the author's interests are, and I love all such head bobbing because it allows me to see where the author is coming from. I've always tried to understand what an author is trying to accomplish, whether or not they actually succeed; in this way, I can properly and justly judge the writer separately from my own preconceptions. (This is unlikely, anyway, but I still give it the old college-try.) 
 We've got a narrator who is a bad-ass who has steeped himself in enough recent (30 year-ish) cultural morass that I'm surprised he didn't become the first 2100 year-old couch potato. Although, I suppose that could be an interesting story in itself. It could be that he's just a fan-boy. The narrator, not just the author; we know that already. My only complaint is that if he is so susceptible to cultural fan-boy-ism, then why doesn't he have a lot more thrown in besides Shakespeare and the more recent stuff? Why not have him get into the Hellfire club and join anarchist book clubs run by fire toting Deists. Oh wait, I'm talking about having the druid be one of America's Founding Fathers. Oh, well, maybe later. :) 
 It's ok, because I know he's aimed at being relevant to today's readers, and I can forgive a lot as long as it remains entertaining. It does so, very much so. This book is probably my favorite of the 
 series, so far.