what are the main features of romantic poetry?
I'll focus this answer on English poetry of the Romantic Period, which extends from about 1795 to 1875.
Poets like Wordsworth, Coleridge, Shelley, Keats, Byron and others, in a reaction to the rational, scientific, mechanistic view of the world depicted in the literature of the eighteenth century, began to emphasize concepts like sensibility (how one feels about life); love of nature; a return to primitivism and an interest in the past (for example, the Celtic revival); mysticism and an interest in the individual.
We have poems like Wordsworth's "Tintern Abbey," which speaks to the poet's re-invigorated interest in nature after viewing the ruins of a medieval abbey, Coleridge's "Rime of the Ancient Mariner," which is, in part, about the mis-use of nature and the cost of ignoring nature's help, Byron's "Childe Harold's Pilgrimage," taking as its model the medieval romance and as its subject the self-realization of the individual. Each of these is in almost direct opposition to the highly-structured poetry of the eighteenth century that dealt with societal and cultural issues rather than the development of the individual as the Romantics did.
The Romantic Period poets tended to focus on an individual's experience in the world, and so their poetry tried to analyze a person's unique experiences and attitudes toward those experience rather than make generalizations about society's experience or attitudes.