If you want to better understand the poetry of W. H. Auden, and you want to buy only one book of Auden criticism, buy this one. (If you want to get a second and third, buy Mendelson's _Early Auden_ and _Later Auden_.) Fuller succinctly but comprehensively explains every poem Auden ever published. Fuller's treatment pays careful attention to poetic form, literary allusions, contemporary sources, and the development of Auden's poetic sensibilities, including his subsequent revisions of many poems. This is not to say that Fuller's commentary is the last word on any one poem, but he consistently enlightening in his comments, even for readers who are already very familiar with Auden's poetry.
One difficult decision that Fuller evidently had to make early on was how to organize his work. He might have organized it any number of ways, but he opted to order his book according to each volume of poetry Auden published. Originally, that was the right decision. Most early readers of Auden bought his books as they appeared, and since each volume originally stood as an aesthetic whole, Fuller's choice made perfect sense. However, now that a new generation of Auden readers (myself included) is reading Auden through anthologies and through his _Selected Poems_ and _Collected Poems_ (edited by Mendelson), Fuller's commentary can be difficult to use, partly because he does not usually use the titles that Auden later appended to many of his earlier poems. However, that minor inconvenience is more than compensated for by the extensive index.
One of Fuller's best qualities is his lucid prose. One does not have to be a trained literary critic to understand Fuller's writing, which is generally forthright and clear.