Michael W. Mayfield
1 Book lacks important details
This book has a lot of strong points, but the maps are poor and so are the driving directions. Basically I can't help thinking that the authors want to tantalize paddlers into coming to Costa Rica, but they do not want to empower them to put together their own trip. The other reviewer noted correctly above that one of the authors owns a rafting/kayaking tour company. Of course they don't want you to be able to put together your own trip.
2 The definitive guide on a Costa Rican Paddling
This book is is slightly dated - a revision is in the works from what I can tell of Web based updates.It is still the most comprehensive and detailed guide available to both kayakers and rafters (although it is written primarily for kayakers). Dozens of rivers are covered as well as many of their indvidual rapids, peculiarities, specifications, and best times to run. By teaming a scientist up with Raphael Gallo (paddler and President of one of the top river outfitters in Costa Rica - Rios Tropicales) you get a balance of technical information as well as practical information with some good photos to boot. This book is mandatory if you are a serious paddler who wishes to explore Costa Rica.