Very entertaining, energetic read. Ms. Ball is quite passionate about her chosen subject, even going to the lengths of trying to recreate some of the items she writes about (with varying degrees of success - some of which have quite humorous "calamities" associated with them). A lot of material is presented. A LOT. This is not a book you read and then put away never to look at again. If you want to get it right when working on your story, you're going to have to pull this book out and use it as a reference. Unless you have an amazing memory, you're just not going to be able to file away all of the tidbits of information Ms. Ball writes about.
To some extent, the difficulty in remembering all of the material is due to how the material is presented. Within each topic, the author often bounces around time periods, making it difficult to remember what was available when. You'll want to look over the information in question and verify what/when/where it was available and how it was used. Appendix I in the back is of immense help in keeping seasonal track of what your folks were harvesting, eating and or preserving. Appendix II is useful as an example of what items might be required, and in what quantities, for you medieval noble to put on a proper feast. The book ends with some useful reading suggestions, some of which I may try to hunt down.
In addition to basic food information, Ms. Ball also discusses herbs, medicine and disinfectants, preservation, cooking methods, storage, domestic animals, the politics and social norms associated with food, and even the complications of feeding an army.
Definitely worth reading and keeping as a reference book.