Let me be clear: I love me some Michael McBride. When he's on point, he's among the best thriller/horror writers out there. Unfortunately, Xibalba is not an example of his usual pointy-ness.
Dealing with a crew of scientists and their diving-spelunker guide who find some very scientific things to get very scientifically excited about, McBride, as his style, spends a lot of pages nailing down the fact that he is a peerless-researcher. His knowledge of the subject matter is exemplary, and I can't recall the last time I had to check an on-line dictionary as often as I did while reading this one.
But this technical detail comes at the significant price of grinding any narrative momentum into the ground. This book is almost literally 90% set-up and 10% payoff. To be lazy, it's the novella equivalent of the first Paranormal Activity film: Not much, nothing, nada, oh a bite!, set-up, more set-up, back to nada, WHAM! (caught you napping!), death, dismemberment, slight twist, fin.
Disappointing in the extreme, I have to say Xibalha is the worst McBride story I've yet read. But I'll be back for more - because when this writer is good, he is simply spectacular.
2 Careless Researchers Not Researching Their Destination for Xibalba.