George Romney is remembered today - if at all - as a society portraitist. But his drawing A Moonlit Sky, one of the highlights in a brilliant show, lights a way to the land of the unconscious. Romney's drawing, done in the 1780s or 1790s in the age of early romanticism, depicts a black felt sky in which the half-veiled moon floats out of dreams and folklore. It has the mysticism of Blake, the precision of Constable and a delicate sensibility all its own.

In a Self-Portrait from 1784, Romney looks at us steadily yet sadly. Painted in flimsy pinks and greys, it is deliberately unfinished, as if he is not all there. The artist presents himself to us as an impotent, vague figure, like Laurence Sterne's Tristram Shandy. Did he see himself as a failure? If so, his contemporaries never guessed.

In his time, Romney was the most fashionable portrait painter in London. Commissioned to paint the future Emma Hamilton, he went on to depict her many times in different costumes and settings. But he got too close to the flame of 18th-century pop culture; after his death in 1802 he was pigeonholed as a sentimentalist.

Alex Kidson, the exhibition's curator, catapults Romney to where he belongs: among the great names of British art. After seeing Romney's drawings we look differently at his portraits. Here is a boy in a red coat, sometimes said to be William Pitt. He is sprawled in a woodland with aristocratic confidence, and yet the woods and clouds are painted with a romantic strangeness, suggesting the realm of the psyche behind the child's serious eyes.

Romney saw under the surface, perhaps because there was more to him than met the eye. In his imagination he was a romantic celebrant of the woods and sky. The gap between his ambitions and the career it was possible to have as a painter in 18th-century Britain is the source of the sense of failure we glimpse in his Self-Portrait. This exhibition finally lets Romney be the artist he knew he was.

· Until April 21. Details: 0151-207 0001.