Romanticism in Art: Central Themes 

"a sweeping but indispensable modern term applied to the profound shift in Western attitudes to art and human creativity that dominated much of European culture in the first half of the 19th century, and that has shaped most subsequent developments in literature--even those reacting against it. In its most coherent early form, as it emerged in the 1790s in Germany and Britain, and in the 1820s in France and elsewhere, it is known as the Romantic Movement or Romantic Revival [like "Gothic"--reflecting a return to old, old stuff--of the Goths or myths of Rome]. Its chief emphasis was upon freedom of individual self-expression: sincerity, spontaneity, and originality became the new standards in literature, replacing the decorous imitation of classical models favoured by 18th-century neoclassicism. Rejecting the ordered rationality of the Enlightenment as mechanical, impersonal, and artificial, the Romantics turned to the emotional directness of personal experience and to the boundlessness of individual imagination and aspiration. Increasingly independent of the declining system of aristocratic patronage, they saw themselves as free spirits expressing their own imaginative truths; several found admirers ready to hero-worship the artist as a genius or prophet. The restrained balance valued in 18th-century culture was abandoned in favour of emotional intensity, often taken to extremes of raptures, nostalgia (for childhood or the past), horror, melancholy, or sentimentality. ... almost all showed a new interest in the irrational realms of dream and delirium or of folk superstition and legend. The creative imagination occupied the center of Romantic views of art, which replaced the `mechanical' rules of conventional form with an `organic' principle of natural growth and free development"

(Chris Baldick, The Concise Oxford Dictionary of Literary Terms [New York: Oxford University Press, 1991], s.v.).

For a longer explanation, go here.