F.R. Leavis was the most influential literary critic of the English-speaking world in the mid-20th century, and Revaluation, first published in 1936, is the book that made his name. In the years since, especially with the rise of postmodernism, his style and assumptions have become so unfashionable that to encounter them again is positively exhilarating. Think of Leavis as literary criticism's Roy Orbison--so square, he's hip.
This book surveys a vast swath of English poetry, from Donne to the Victorian Romantics. It famously upgrades Donne and Marvell while showing skepticism towards Milton, and offers a complex treatment of the "holy trinity" of Wordsworth, Shelley, and Keats. Above all, though, it's the best exemplar of Leavis's modus operandi: take particular poems by particular poets, add a rich appreciation of their historical and social circumstances, and try to make convincing judgments about their achievements without deferring to some overarching theory.
Undoubtedly, the Leavis style has dated; if it struck some contemporaries as pedantic and heavy-handed, it seems even more so now. Yet the language is subtle, capable of convoluted yet precise sentences that make unexpected distinctions sharply. Look, for example, at his brilliant analysis of the difference between good and plodding excerpts from Paradise Lost. --Richard Farr