Excellent, excellent format. You get an introduction to each poem, and a verse by verse explanation on one page with the verses in English running parallel on the other. It is all very simple and approachable. It doesn't go into deep theology or linguistics, it just tells you what you need to know.
It feels like more of a commercial product for the curious reader than something for the serious student. But this clarity and approachability are its greatest strengths. It is also a really well presented book. The cover is attractive and it is good quality.
West has provided a wonderful, insightful and under stable translation of the Gathas of Zarathushtra. Removing the misleading Ahura Mazda title he has allowed readers of belief and non-belief to understand the spiritual journey and prayers detailing that journey of this phenomenal Bactrian prophet. The translated texts are presented in very readable and understandable form opposite clear but concise notes on their meaning and relevance. Although a book of scholarship these translations could be equally used for recitation or indeed meditative reflection. Excellent. There is so little available on these texts in English and so little that is to date that this work is indeed a treasure. A useful parallel translation and introduction in by Humbach.
These translations are an attempt by M. L. West to understand Zoroaster and his life, using the comparative Indo-European evidence to fill in blanks left empty by other translations. West is clear in his belief that Zoroaster was a real man who lived in western Afghanistan about 2600 years ago, and who composed a set of hymns (those translated in the book) while founding a religious sect using those orally-composed hymns as scripture. It was this sect and these hymns that became the dominant, but not sole, religion of Persia from the Achaemenids to the end of Sasanian rule in the wake of the Arab invasion, and it is fascinating to see how the cow-loving, compassionate, sort-of-monotheistic religion of Zoroaster became something else entirely as the needs of the Persians who had adopted it changed.
The translations of the yasnas, the hymns, are accompanied by notes by West explaining each verse and its relation both to the hymn as a whole and to the rest of Zoroaster's extant oeuvre. A Zoroastrian liturgical text is also translated. The introduction makes much of the precision of the oral mode of transmission, noting that the accuracy of the Zoroastrian priests who had memorised Zoroaster's hymns was greater than the fidelity of many manuscript traditions.
This translation is a perfect companion to the Rigveda, and I'd recommend reading each side-by-side.