Inventing Impressionism: The National Gallery's latest blockbuster is devoted to the art dealer who popularised the movement

Inventing Impressionism, Paul Durand-Ruel and the Modern Art Market is the latest in a series of National Gallery blockbusters. Focusing on Durand-Ruel, an art dealer who has been credited with discovering and nurturing Impressionism. This has been organised in a "modern way", a manner designed to bring in a new and, I suspect, a younger audience.

The wall texts paint a picture of a man who was often forced to leverage his passion into a lucrative business. The son of a dealer himself he raised his children and grandchildren to join the business. Fortunate enough to run into Monet and Pissarro in London, Durand-Ruel placed them both on retainer and the rest is history. According to the premise of the exhibition, Impressionism was a hard act to sell and without the singular determination of the dealer our art history might be quite different. If I sound cynical it is sad because there are spectacular objects for the art lover to discover.

The first room sets the scene, with a portrait of Durand-Ruel painted by Renoir in 1910. Here the dealer and art lover is painted by one of his most loyal artists and long-time friend. The colours are more mellow and the mood and tone more introspective then Renoir's usual portraits. In an earlier work by Renoir of 1882, Durand-Ruel's daughters are painted in a garden in his more recognisable spring-like pastel tones. There are two full-length paintings from his series Dance in the City and Dance in the Country, which both hung in the grand salon of Durand-Ruel's grand Parisian apartment, and again remind the viewer that Renoir was more capable then merely capturing chocolate box portraits.

A set of doors taken from Durand-Ruel's house is also included. He had commissioned Monet to decorate them and the panels are painted with a variety of delightful images designed to show the range of the artist's skills with fruit and flowers. Nearby is a gleaming marble Rodin carving of a mother and child; a similar one apparently graced the dealer's mantelpiece.

There is no doubt that Durand-Ruel had a prescient eye, and he was soon investing in Edouard Manet, a painter who was better known at this time for his notorious and well-publicised rejections from the Paris Salon than his illustrious sales. Durand-Ruel splurged on a wonderful work, The Battle of the U.S.S Kearsarge and the C.S.S Alabama (1864). Manet vividly brings the warships to life. More remarkable perhaps, as Manet did not witness the event, but re-created it from newspaper reports. Nearby, a tasty still life, The Salmon (1869), illustrates the artist's ability to not only paint impactful war scenes and sensitive portraits but also still lifes of wonderful skill, validating the dealer's interest in this artist.

By 1876 Durand-Ruel had weathered yet another financial crisis and lent his galleries out for the Second Exhibition of Impressionism, while the critical response was subdued and the sales poor, his name was now inextricably linked with the group.

Looking away from the gloomy wall charts to the walls themselves we see a marvel of epicurean discrimination. Edgar Degas' Peasant Girls Bathing in the Sea at Dusk (c1869-75) shows a bold experimental artist unafraid of his subject matter, allowing the work to appear unfinished in the best "modern" sense. Bare canvas peers through as the girls cavort, hands clasped, silhouetted against a rich colourful sky, the dryness of the paint making the figures appear more frieze like, then painted in juicy impasto. Displayed in the exhibition it was also the most critically damned, leading to a contemporary critic denouncing Degas as "the most intransigent of an intransigent company". If you think you know Degas then this is a painting that shows a different, radical side.

Discoveries continue. There is a still life, The Galettes (1882) by Monet, which had my mouth watering. I am gratified to discover that it was owned by a master pâtissier in Pourville, France. The plump, well-browned cakes and wine invite the viewer to taste with their eyes. Further on Pears and Grapes (1840), another still life of assembled fruits, reminds us that there are also parts of Monet's oevre far from landscapes and haystacks. Sadly we are told that Monet turned to these subjects as they were easier to sell. To remind us of his serial works there is a stunning wall of poplar trees, an unsurprising favourite subject of his peers. Here, reunited from collections from around the world from Tokyo to Paris to Philadelphia, they remind us that serial painting is not dull in the right hands, and that an ordinary line of trees can reward careful scrutiny.

Monet was able to paint the atmosphere of a sublime sunny day but The Train in the Snow (1875) literally chills the spectator, the steam of the air coalescing in the cold air already thickened with snow.

One of the wall texts remind us that without the collectors of the US, Durand-Ruel would have been financially ruined. In the final rooms, we see examples from the great museums in America, the Chicago Art Institute, The Boston Museum of Fine Art and The Philadelphia Museum of Fine Art where American collectors discovered, in particular, the delights of Renoir. In Dance at Bougival (1883), a full-length painting that mirrors the earlier examples, a couple dancing are lost in each other, the detritus of cigarette ends at their feet ignored in their delight of movement.

One of my favourite paintings in the show is by the American artist Mary Cassatt. The Child's Bath (1893) portrays the intimate trusting moment of a mother bathing her child's feet. Along with Berthe Morisot, Cassatt is also one of only two women artists in the show. The accompanying guide says that Cassatt was also key to Durand-Ruel, introducing him to many patrons as well as members of her own wealthy family, reducing somehow this painting to merely a financial deal by a talented rich woman. Next to it hangs The Ballet Class (c1871-74), an easily recognisable work by Edgar Degas. The scene is a lesson in a ballet school: awkward young girls with a uninterested mother reading a newspaper in the foreground.

By now you will have noticed my antipathy to the bordering-on-crass premise of this show. It should be enough that Durand-Ruel had a wonderful eye and bought paintings to make both his and others' hearts quicken. There are unusual choices sometimes, too, as with both the Degas and the large late landscape by Théodore Rousseau, an artist whom he had invested in heavily. A View of Mont Blanc, Seen from La Faucille perfectly captures the crystalline light of mountain air, and a small group of figures in the foreground places the whole work in human scale. Next to it, a mysterious night-time view, The Sheepfold, Moonlight by Jean-François Millet, captures the romanticism of Impressionism without the potential of chocolate box sweetness.

There are wondrous things to see here, including the sheer humour of the juxtaposition of two wonderful Gustave Courbet paintings. Woman in the Waves (1868), a depiction of the goddess Venus emerging from the sea, naked with pert lovingly painted breasts, is juxtaposed with Courbet's still life, a study of apples, their roundness reprising the breasts of Venus perfectly. Courbet painted this cornucopia of fruit while in prison serving time for his politics and role in the revolutionary Paris Commune of 1871.

A guard says to me how happy he is to see some colour in the gallery after the sheer unrelenting brown-ness of Rembrandt, and I smile inwardly, thinking of the similarities of the difficult reception of these artists' works during their respective lifetimes. How Rembrandt was also rejected by his artistic peers. How a Monet that we look at now looks so familiar and acceptable, but was so new and difficult at its time. How Manet struggled with multiple rejections, perhaps money and power need to be rewarded with the recognition of how this art was elevated by a dealer, I only wish our nose had not been rubbed in this theory so often. Do not allow my quibbles about presentation to prevent you from enjoying the treasures in this wonderful show.

Inventing Impressionism, Paul Durand-Ruel and the Modern Art Market, National Gallery, London WC2 (020 7747 2885) to 31 May