I read this book a few years ago, but wanted to re-read it so that I could write a review. It was better than I remembered, but still not very stellar.
I felt like this is three stories interlayed within each other (possibly in part because Egan can't deal with a full length novel? Goon Squad is also just shorts pulled together with a few threads), rather than a real novel. She tries to create tension between the three layers (Danny & Mick, Ray, and Holly), but I didn't really sympathize with any of the characters. I think the whole Mick is Ray was supposed to surprise the reader, but I just didn't care enough.
As for the text itself, I did not like Ray drawing attention to himself within the story of Danny. I think I would have preferred it to start with Ray and then pull in the Danny layer. While the invention of words was cute, I didn't think it was completely necessary (and annoying that the best Holly can do is borrow Danny's word "alto", but give it a new definition). I am also more than 90% certain that a Stephen King character somewhere uses "the worm" as a label for the psychosis into which he falls (which is the same usage here, but no reference to Stephen King).
I did enjoy that the cousins are Howard and Danny King; and so the Kings take the castle over by outsmarting the baronness. Just a cute naming device.
I thought the whole romp in the tunnels was ridiculous on several levels. First, Danny is recovering from his concussion and his leg injury; he would be unable to go on the expedition, let alone carry Benjy around. Second, the motivation is poor; if Howard still has some residue of fear from being left in the cave as a kid (and clearly he does), then why would he be so excited to go trekking along and wouldn't he be more likely to want Benjy not to come (save his child from trauma). Third, Egan rambles along about the power shift from Howard to Danny after they get out; but this is not when the shift comes. The shift in power is in the tunnell when Howard looses his shit, but Danny leads the group. At that point, Danny has the power. Once they are back above ground, Howard is back in power; after all, he is the one with all the cash. Danny has a bit more respect and appreciation, but he is still powerless. Until, of course, the moment that Howard suggests making him a partner at which point Mick/Ray kills him.
There was one great quote about American love of electronics/consumer culture: "People are bored. They're dead! Go to a shopping mall and check out the faces. I did this for years--I'd drive out to the malls on weekends and just sit there watching people, trying to figure it out. What's missing? What do they need? What's the next step? And then I got it: imagination. We've lost the ability to make things up. We've farmed out that job to the entertainment industry, and we sit around and drool on ourselves while they do it for us."
Overall, nothing fantastic, but easy entertaining and an easy, quick read.