The Digha Nikaya was apparently the first portion of the Pali Canon to be recited after the Buddha's passing and contains some of his most important discourses. This book compresses all 30 odd discourses (suttas) into a relatively slim volume compared to the original with its repetitions which would run into tens of volumes.
The only alternative to this edition which is reputable is still probably Rhys David's translation for the PTS in 3 volumes which is actually good but archaic, harder and pricier to get hold of.
Walshe's translation reads easily and his notes are quite chatty but a few of his comments could have been avoided. The Buddha comes across as quite human is his speech and earnest in conveying something to his listeners (the English is highly readable and fairly simple as opposed to older and archaic rendering), commanding as usual but cool and detached with a tremendous sense of compassion.
More abstruse passages within certain suttas will not be understood by most readers without meditation practice or guidance from teachers and the book itself lacks sufficient explanation, in fact some elements of the translation may be wrong or mis-interpretted.
This book is a boon companion for anyone who feels s/he needs the highest security.
Most of the suttas here are applicable to lay people as well as monks (the usual audience the Buddha addressed) and this volume contains seminal discourses such as 1. The Great Discourse on the foundations of mindfulness, 2. The discourse of the Great decease of the Buddha and 3. Fruits of the homeless life. There are many others such as one specifically as to how lay-people should live and guard their worldly affairs and at least two dealing with gods or conversations with celestial beings.
I think this book represents an excellent reference for the price and can be read aloud when you are alone. Profound, mysterious, to the heart and yet sometimes extreme or humourous. As Nyanaponika says (the late) "Mr Walshe has done an excellent job".
Although some reviewers emphasis is on the scholarship or the translation, this book contains chiefly the values of Buddhism as taught by the Buddha Gotama. Because it contains an important part of the Buddha Gotama's life, it is long, and in the same style as Gotama taught : parabola's, metaphors,...and with a very strong taste of aryan culture....hence it not easy for westerners to gather its meaning unambiguously. This is therefore not an introductory book. For that, "The heart of the Buddha's teachings" by Thich Nhat Hanh is probably the best choice to get the substance of the Teachings, since it relies on a wonderful intuitive style. If you prefer a more provocative as well as more sensible version of the Buddhist values, Sanditeva's "Bodhicaryavatara" is strongly recommended...it is shorter, more dense and extraordinary in its depth...up to you to choose the writing style that is the most likely to be fitting to you... Please don't forget to begin with introductory books about Buddhism since getting directly in the values without having a preliminary understanding of the culture will make you loose much of the more advanced books meaning...as always, first the basics to understand where you are going to, then go farther on the path you now clearly see... Take the time to grasp the meaning of every word, compare every "sutta" with your life and your values, it is worth the intellectual effort.