The book, with more than 400 pages, covers all of the major and most of the minor midrashim. For each midrash, Anat reviews the state of research on questions like provenance and text. For each one she provides one or two nice examples of midrashic technique. She also provides bibliographic information on editions and studies.
Earlier versions of some of the chapters can be found here - there's a tab in the sidebar labelled 'Mavo la-Midrashim'.
Reizel's introduction to the midrashim is available now at the Tevunot stand at Shavua ha-Sefer for only 60 shekels. It's also available online for 80 shekels.
Disclosure: the author is an old friend of mine, and I helped a little with the bibliographic aspects of the book. That said, I have no doubt that this is one of the most helpful tools for students and scholars of Midrash to appear in a while. Without purporting to contain original discoveries, it presents a great deal of pertinent information that anyone dealing with the gamut of midrashic literature need but rarely know offhand.