Donne's poetry is of the Metaphysical school. It's a kind of pre-Romantic poetry similar to the Elizabethans', namely Shakespeare's, who used many conceits and extended metaphors like Donne. Donne's poetry can be divided into two stages: early Donne (focus on physical union) and late Donne (focus on spiritual union). Early Donne is sexually suggestive, and he paves the way for Andrew Marvell's "Coy Mistress" and the eros of the pre-Romantics of the Elizabethan era.
In terms of style, Donne's poetry is not as metrical as Shakespeare's. Donne's verse is much more uneven and jarring to the ear. Early Donne wrote in an open form; Shakespeare was more closed (sonnets). Shakespeare's verse, with its iambic pentameter, is much more uniform and euphonious.
Donne's major themes in his earlier period are similar to Shakespeare's: physical union. Both poets' speakers want to live on either in the physical act of love or in the memory of their lovers. Later, Donne will focus on spiritual union. His later poetry will sound and look more like the Cavaliers.
The Cavalier poets, followers of Ben Johnson, broke from the Metaphysical poets during the Elizabethan era. Johnson was a professional writer, unlike Donne. His major themes were art, order, development of good character. Johnson and his Cavaliers wrote more fixed, closed-forms of poetry: elegies, epitaphs, tributes, lyrics, epigrams. These Cavaliers seem to be the forerunners of the Realists, as opposed to Donne as a forerunner of the Romantics.