Not what I had hoped--which was for this to be an Ireland-only extension of the well-done The Atlas of Literature, which was actually be a better tool for my purposes than this book.
My purpose, and hope for this book, was to match the literature to the landscape, showing the counties, towns, and countrysides where writers and their voices and ideas originated, kind of a walking tour of the Ireland of James Joyce, St. Patrick, and other famous Irish writers.
As you can tell by my namechecking of two Irish historical characters that anyone would know, I am not a knowledgable Iro-phile, but rather a reader interested in and wanting to know more about the authors and landscape of Ireland. Trevor's book would be better for those already familiar with the landscape, as he assumes a fair level of background knowledge in Irish history, never really places the settings in a atlas-friendly way (there is a rudimentary map in the beginning, but it is never referenced by the author), and doesn't systematically (by date, style, gender, or geographic roots) place the authors he references or quotes. If this is what you are looking for as well, go to the previously reference Atlas of Literature.
There are some nice old black and white (and a few color) pictures throughout, and they provide most of the interest I was able to generate in the book as I skimmed over the long quotes from obscure (to me, at least) Irish poems.