The Courtauld Institute of Art consists of two main components: a world-renowned college dedicated to the study of art history and conservation, and a gallery housing a staggering collection of masterpieces, including Manet's A Bar at the Folies-Bergère, Botticelli's The Trinity With Saints, and Van Gogh's Self-Portrait With Bandaged Ear.

The two were held in the north wing of Somerset House in London, a majestic 225-year-old building created for King George III by architect William Chambers, until renovations began in 2018. It's a structure whose tidy exteriors conceal complicated innards designed around the many government agencies and learned organizations it was meant to host.

The gallery will return to the public next week after a renovation that aims to highlight the old building's glories and quirks while also showcasing the art to its greatest advantage. It's also part of a project called Courtauld Connects, which aims to bring the gallery, the college, and the general public closer together.

The project has so far cost £57 million, which covers the building expenditure as well as "broader costs" including public engagement and offsite art storage. The students and employees will be rehoused alongside the gallery in a second phase, which will take place near King's Cross station.

Everything about it seems to be fantastic. Dedicated teams of artisans have worked with extreme attention and care on the delicate and intricate ancient cloth. They were headed by competent architects Witherford Watson Mann, the Stirling Prize winners.

On the gallery walls are the names of a dazzling array of blue-chip donors: Ukranian-born oil and media mogul Leonard Blavatnik, the Garfield Weston Foundation, and the luxury brand empire LVMH.

While some of the remodeling is great, a series of bizarre decisions prevent it from being the revolutionary undertaking that the promises and finances may suggest.

The architects' solution to the need for connectedness is a "circuit of shared exchanges," a method of navigating through the building that stimulates interaction between its many purposes and users. The building's prime exhibition room, the 18th-century Great Room, has been transformed into the home of its major displays, the impressionists and post-impressionists.

A dramatic area has been hollowed out of previously hidden vaults in the basement, where a café servicing both the gallery and the college was intended. Two magnificent semicircular staircases, part of Chambers' original construction, connect the two.

Between the majestic attic and noble cellar is a sandwich of many volumes, including the Fine Rooms, which are rich in ornate plasterwork, as well as more basic offices and backup facilities that have been converted to exhibit art. New educational and exhibition rooms have been crammed in where possible: since this Grade I-listed building cannot be extended, the most of the volumes inside its walls and roof have to be made.

It took a lot of work to make it seem as though there was little effort involved. Old doors have been remodeled such that when they are open, they fold neatly into the thickness of the wall. The many ducts and wires required to supply an art gallery are hidden in ceiling spaces, making them almost invisible.

This swan swimming under the surface has taken a lot of time and effort. It's an exceptional instance of the magic that occurs when big pieces of masonry are bashed and shifted, and massive steel beams are lifted, finally devolving into mouldings and details of wood and plaster, where millimetre-level choices make a difference in the feel of a space. The vestibule, which is Somerset House's sophisticated, domed entry, has antique diamond-patterned pavement that has been folded into a gentle slope that allows wheelchair users to approach the gallery's main door. It's a subtle change executed with finesse and elegance.

You might claim that the project demonstrates how tens of millions of dollars may be spent without anybody noticing. That's partially a good thing, since self-aggrandizing architectural gestures aren't something you want. Art and old architecture are both more essential than contemporary ego.

However, after so much effort has gone into subtlety and inconspicuous improvement, a sequence of choices have thrown them into disarray. At the same time, it seems that the ambition of combining the gallery and the institution has all but died.

To provide just one tiny but important example, the stairwells and circulation areas have been outfitted with cheap white rectangular light fixtures that would be more at home in a cheap hotel's escape routes. To take a broader example, the subterranean vaults do not, in fact, house a café where the general public may mingle with students and intellectuals, but rather a massive store with plywood shelves and mounds of merchandise that will obliterate the building's otherwise meticulous detailing.

Other issues, such as the allocation of space, are also debatable. The impressionists now have plenty of volume and headroom without seeming to profit – I'm not convinced they sing any better than they did in smaller spaces – whereas medieval art is confined to a small, low-ceilinged space. Some of the new galleries have been painstakingly cut out of ancient cloth, making you question whether the effort was worthwhile.

Above all, the gallery and college seem to be farther separated than ever, with the latter essentially relegated to a different site until such time as sufficient financing is found to bring it back to Somerset House. The declared goal of reconnection does not seem to have been rigorously followed; the present product appears to be more like the exaltation of the partnership's more glamorous element, the gallery, at the detriment of the other. The good news is that behind it all, there is some clever architecture. However, it requires more knowledge to bring forth its hidden abilities.

Thanks to Rowan Moore at The Guardian whose reporting provided the original basis for this story.