This highly anticipated book could have been ground breaking in showing people how to cook using ratios of ingredients (e.g. one part sugar to two parts fat to three parts flour = a basic cookie dough) rather than slavishly following recipes that always seem to be different from each other. Traditionally, cooks used this sort of knowledge all the time but most home cooks nowadays seem to have lost it.
So, the concept for this book was great. Ruhlman's engaging text and delicious recipes, his tips and advice, all make parts of Ratio valuable. He clearly explains the strength of concentrating on relationships between ingredients rather than individual quantities, and doesn't pretend that understanding ratios makes you a good cook -- he reminds the reader that making good food comes down to experience and execution.
Unfortunately, the good bits are overshadowed by text that I felt was confused, inconsistent and highly repetitive. There was a lack of clarity in explanation and that stood out as a failure in such a conceptually important work. There are no diagrams beyond a sort of "wheel" of ratios. Most ratios in the book are based on weight, but Ruhlman is inconsistent about this as the book progresses, and in the recipes. Through it all, I longed for the knowledge of cooks experienced in the old ways of cooking by ratio/proportion/quantity, rather than a chef's spreadsheet (the inspiration for Ruhlman's book).
I've written a much longer review on my own site, so I'll just round off here by saying Ratio is a great concept but I feel it is best suited for readers seeking inspiration rather than clarity or careful explanation.