This is a terrific book, but I do have some reservations. What is so terrific about it is that it is jam-packed with information useful to any bicyclist planning, or in the middle of, a trip along the Rhine River. It includes sections on equipment, geography, history, money, climate, foreign words and phrases, etc., as well as detailed routes, alternate routes, and "diversion routes" (with maps) along the Rhine. Of course, one could bring along a pack of books on all these topics, but any traveling bicyclist is obviously greatly limited as to what he/she can carry. So it's nice to have so much information in one place. Naturally the longest part of the book is devoted to Germany, as this is the longest (and probably most interesting) stretch of the river.
I traveled my own "Rhine journey" by bicycle (the Netherlands, Germany, France, Switzerland) a few years ago, and it was one of the most memorable events of my life. I kept a detailed diary at the time (highly recommended), and frequently still turn to it. John Powell's book also brought back many happy memories.
My quibbles (mostly minor) about Powell's book are as follows: I found that for each route, the number of tiny instructions offered to the bicyclist seem obsessively detailed, almost to the point of being funny. For just one example, to bicycle from Bacharach to Mainz, a very simple stretch of 37 miles, all on the western side of the river, Powell offers more than 90 instructions! Long-distance bicyclists are a pretty resourceful and intrepid lot, really don't need this kind of detail, and rarely get lost. I myself bicycled the entire Rhine route with just good maps, notes I made at home before I left (about places and sights), and a small guide to youth hostels. And I never got lost!
Speaking about youth hostels, most long-distance bicyclists in Europe are relatively young and stay in hostels along the way. Hostels are usually fun, cheap, and a good way to exchange travel tips and make friends. Powell devotes very little space to them. A hostel guide is very useful in planning. The one from the Deutsches Jugendherbergswerk in Detmold is great, also "Hostels Germany" by Paul Karr and Martha Coombs is useful and fun.
A tiny point: Powell says, regarding bicycle tires, that he uses "slick (smooth) treads for better speed." What's the hurry? Why not slow down a bit and enjoy the marvelous scenery? Also, I think a somewhat thicker tread is advisable, unless one is adept at fixing flat tires (not all the bike paths are free of sharp pebbles and glass!).
Powell's book is a thoughtful guide, obviously not a book to sit down and read cover to cover, but a good resource for planning or executing that trip along the Rhine. If you do make the trip, I hope you have as great a time as I did!