Yeats considered Donne a great poet. Yet Donne was Yeats' master, and his greatness depends on no one's claims. To read Donne's verse is to be alive. Scholar, pastor, lover—his many personae frequently surface, and frequently render the reader speechless with their profundity and beauty.
Donne's poems are visceral, accurate, intensely personal, divorced from artifice. When he says to his mistress "O, my America, my Newfoundland!" we almost squirm at the intimacy of it; and when he says to the Creator "Batter my heart, three person'd God" we yearn with him for spiritual renewal and realization.
Donne manages to capture man's true state, both our physicality and spirituality. In the depths of lust his lines are earthy, vigorous; when reflecting on his own sinfulness they are anguished; and the poems about God are fearful, worshipful, mysterious. As a metaphysical poet, he was concerned not just with the beauty of poetry, but with its capacity to reflect and comment on existence. That he never becomes tawdry or baldly didactic is testament to his brilliance.
Some people read Donne in place of devotions, but you could just as easily read him for the opposite effect. Before he was a devout Protestant minister, he was a womanizing profligate, and both identities emerge in the poems. Hymns to the flesh and hymns to the Divine stand together, each end of the human experience brought to adroit synthesis by a man preoccupied with death, love, sex and God. It wasn't until the 20th century that Donne's genius became fully appreciated—since then he has generally been heralded as one of, if not the greatest English poet of all time.