If you've never read it, and you have a vague sense that your education is somehow incomplete and you'd like to remedy that, this is your book. Period.
Others might scoff at my literary ignorance, but I was really impressed by Adler and Van Doren's suggestion that the Great Books should be read chronologically, in order to take part in this "Great Conversation" that has been going on since man learned how to write. Previously, I had regarded the Great Books as so many individual stars in a literary universe, with absolutely no rhyme or reason on where to begin reading. However, now, I am approaching these classics in a more disciplined way by following a chronological reading list, and this has added a dimension of understanding to my reading that I really had not encountered before.
Adler and Van Doren say a lot in this book that I agree with, and previous reviewers have done a good job of summarizing the levels of reading, and the activities associated with them. However, I felt that the authors' suggestions for reading fiction were a bit vague and insufficient. For example, Adler and Van Doren say that the "truth" of a work of fiction is determined by its beauty to the reader, and the reader should be able to point out in the book the source of this beauty. Such a suggestion leaves a lot of things left unsaid and I felt that the authors could have commented a little more on how the reader could go about analyzing imaginative literature.
Nevertheless, this book is a classic. If you consider yourself a serious reader, but have never been formally instructed in how to engage books, then I highly, wholeheartedly, and absolutely recommend that you read this book.