The Courtauld Institute of Art has two main elements: a world-famous college for the study of the history and the conservation of art and a gallery with a boggling collection of masterpieces: Manet’s A Bar at the Folies-Bergère, Botticelli’s The Trinity With Saints, Van Gogh’s Self-Portrait With Bandaged Ear. Until renovation works started in 2018, the two were housed in the north wing of Somerset House in London, the grand 225-year-old complex designed for King George III by the architect William Chambers. It’s a building whose orderly facades belie convoluted interiors that were shaped around the multiple government offices and learned societies that it was built to house. Next week, the gallery reopens to the public after a makeover that seeks to make the most of the historic building’s glories and oddities and show the art to its best advantage. It’s also part of a plan, called Courtauld Connects, whereby the gallery, the college and the general public are supposed to be brought closer together. So far the project has cost £57m, a figure that includes both the construction budget and “wider costs” such as public outreach and offsite art storage. A second phase is planned to rehouse the students and staff – who are currently decanted to premises near King’s Cross station – alongside the gallery. Everything about it sounds great. Dedicated teams of craftspeople have attended to the sensitive and complicated historic fabric with scrupulous patience and care. They have been guided by skilled architects, the Stirling prize winners Witherford Watson Mann. The names of a glittering array of blue-chip donors appear on the gallery walls: the Ukranian-born oil and media magnate Leonard Blavatnik, the Garfield Weston Foundation, the luxury brand empire LVMH. Some of the renovation is indeed exceptional, but a series of perverse choices also stop it being the transformative project that the promises and budgets might lead you to expect. The architects’ response to the call for connectivity is what they call a “circuit of shared exchanges”, a way of moving round the building that encourages its different uses and users to interact. On the top floor, the 18th-century Great Room – the building’s star exhibition space – has been made the home of its star exhibits, the impressionists and post-impressionists. In the basement, a dramatic space has been hollowed out of formerly unseen vaults, where a cafe serving both gallery and college were planned. The two are linked by two elegant semicircular staircases that are part of Chambers’s original building. Between this grand attic and noble cellar is a sandwich of multiple volumes: the Fine Rooms, rich in ornamental plasterwork, plus more humble offices and backup facilities repurposed to show art. New education and exhibition spaces have been squeezed out where possible: as it’s impossible to extend this Grade I-listed building, the most had to be made of the volumes within its walls and roof. A huge amount of effort has gone into making it look as if little effort has been expended. Old doors have been remodelled so that they fold unobtrusively into the thickness of the wall when open. The copious ducts and cables needed to serve an art museum are located in ceiling voids, so that you wouldn’t know they’re there. Considerable craft has gone into this swan paddling under the surface. It is an exemplary demonstration of the magic whereby the bashing and shifting of large chunks of masonry, and the lifting of heavy steel beams, eventually devolve into mouldings and details of timber and plaster, where decisions of a few millimetres make a difference to the feel of a room. A nice moment comes in the vestibule, which is the refined, vaulted entrance to Somerset House as a whole, where historic diamond-patterned paving has been folded into a gentle ramp that enables wheelchair users to access the gallery’s front door. It’s an inconspicuous adjustment done with precision and grace. You could say that the project shows how you can spend tens of millions without anyone much noticing. Which is partly a good thing – you certainly wouldn’t want self-aggrandising architectural gestures. Both the art and the historic building are more important than modern ego. But so much having been invested in subtlety and unobtrusive betterment, a series of decisions undermine them. At the same time the dream of uniting gallery and college seems to have been all but abandoned. To take a small but significant example, the stairs and circulation spaces have been fitted with crude white rectangular light fittings that would belong better on the escape routes of a cheap hotel. To take something larger, those basement vaults do not in fact contain a cafe where the visiting public might mix with students and academics, but a large shop whose plywood shelves and piles of products will make a nonsense of the building’s otherwise careful details. There are other questionable decisions, including about the distribution of space. The impressionists now get abundant volume and headroom without obviously benefiting – I am not sure that they sing any more than they did in less capacious surroundings – while medieval art is consigned to a cramped and low-ceilinged room. Some of the new galleries have been so tortuously carved out of old fabric that you wonder if they were worth the effort. Above all, gallery and college seem further apart than ever, the latter being largely consigned to a different location until the unspecified future when enough funding might be found to bring it back to Somerset House. The stated aim of reconnection does not seem to have been rigorously pursued; the current outcome looks more like the glorification of the more glamorous part of the partnership, the gallery, at the expense of the other. The good news in all this is that there is some thoughtful architecture underneath it all. But it needs more intelligence to bring out its latent qualities.