The massive former docklands development site of Cardiff Bay - once industrial tidal mudflats where colliers berthed, now a service-sector, cultural and political centre on a freshwater lagoon created by a landscaped barrage - has been changing for years. Yet whatever else has been going on, and going up, the opera house site has sat there near the waterfront, next to the equally empty Welsh Assembly site, like a pair of missing front teeth. And now? The opera house is nearly finished and the Welsh Assembly building, by Richard Rogers, is at last starting to appear. We have a result.

Adams is a youngish architect who used to work for Will Alsop, famous for his blob-buildings and stilt-buildings. Though Adams is a far quieter, more emollient character than his old boss, he seems to have picked up some of his maverick tendencies. If you can block out from your mind the memory of what might have been, and instead just look at the Wales Millennium Centre on its own terms, it is a quite extraordinary building.

This is an anti-modern lyric theatre. It rejects not only mainstream international shiny-shoebox modernism, but also the 1980s generation of jokey postmodernism and the much more serious fashionable splintery deconstructivist phase that followed it - in which camp you would have found early Hadid. Still with me? There is also no high-tech glass and steel (Rogers will provide that next door). No white-box minimalism. No billowing Gehry-style curves. Adams has struck all those styles from his list. Instead, what you get is a big bronze helmet stuck on a pile of stones. Or a ship's hull on a ruined castle, if you prefer.

This helmet/hull, made of riveted plates, is the shell of the auditorium. The stones form a stratified curtain wall of rough lumps of slate, occasionally interspersed with seams of laminated glass like threads of crystal. On one side, the slate gives way to tough glossy red bricks not dissimilar to the Victorian Pierhead building nearby. And where the building is not clad in slate or brick or bronze-patinated stainless steel, it is rough timber boarding. If you like your buildings smoothly consistent, you will not like this one. But for all its conscious rejection of fashion and stylistic movements, the Wales Millennium Centre does hit one very powerful current chord in architecture. The buzzword here is "materiality". Which means the rejection of the computer-designed, machine-made look. It's about texture. Stone piled on stone, planks laboriously hammered into place. The working is shown. Part-rural, part-industrial, this particular architectural sensibility has most in common with the Arts and Crafts movement of the late 19th and early 20th centuries, which was very big round here. See Cardiff Castle as reworked by William Burges.