There isn't much question whether Yeats was a great poet, just where on the all time great list he falls. Whether you call him the greatest poet of the 20th century, or the greatest since Wordsworth, Milton or Shakespeare, his accomplishments are clear.
Beyond that, why should anyone buy this edition as opposed to any of the other available? First, the collected poems gives you a sense of his development and interests, not just the highlights of his greates poems. Second, and more importantly, this edition is well-annotated. The notes are thorough without being unduly interpretive--they tell you what an allusion refers to, not how it affects the meaning of the poem. The notes aim to be useful to any reader, regardless of background. As a result, western readers will come across odd sounding notes such as "Jesus Christ is the founder of Christianity" or "Hamlet is the hero of William Shakespeare's tragedy of the same name." Still, you'll be thankful for such prosaic entries as they explain Irish myth and locate historical allusions. All in all, it's an edition that belongs on any poetry lover's shelf.