When Washington Mutual decided to build a new headquarters in downtown Seattle, that gave the Seattle Art Museum an opportunity to fix one of the city's embarrassments: the Robert Venturi design.

For $62 million in 1991, the museum and taxpayers who helped pay for the Venturi building got an architectural belly flop. The building featured an exciting, curved facade and a tireless "Hammering Man" out front, but the inside did little well, except keep rain off paintings. When you entered the thing, you never knew where to go. Once you got anywhere, it felt like a rabbit warren decorated with oversized signage that made sure you remembered the donors. In several respects, the museum's move from its historic home at Volunteer Park was a painful disappointment that was only whispered and regretted.

So when WaMu decided to build a new office tower on the same block, it was a chance to do a joint venture that would open up the Venturi building, correct the pedestrian circulation, add display space, and provide a vehicle for expanded activities. The new building does that superbly, but quietly. As if to compensate for the Venturi's excesses, the new building is understated and almost utilitarian in feel.

The $81 million project that officially opens May 5 was shown to journalists on Thursday, April 26. It is not so much an expansion as an entirely new building that pretty much turns its back on Venturi. Where Venturi went with detailing in stone, the new architect, Brad Cloepfil, goes with a steel-and-glass curtain that defers to its adjoining big brother, the 42-story WaMu tower.

Cloepfil, of Portland's Allied Works Architecture, had a number of tough challenges. Because SAM eventually plans to occupy more space of the WaMu tower, he had to design museum floors to match both the adjoining tower and the old Venturi structure.

The new building strikes me as restrained and careful. It won't be accused of competing with the art. Though the lobby fixes Venturi's mistake by going big, it also seems spare to a fault. There's no ego here, but that has the beneficial effect of putting attention on "Stage One," Cai Guo-Qiang's dazzling work of full size Ford Tauruses, hung from the ceiling and twisting in mid air, with hoses of light exploding from the interior. It's great fun, and a signal that the new SAM has a sense of humor, like Director Mimi Gates and her goofy ties. The Tauruses tumble through the entire lobby. One winds up on the other side of the wall, at rest in the old lobby, an art orphan.

As you walk through the new building, there's an accumulating sense of pleasure. The world has a proper order to things. The rooms flow from one to the other. It's a museum that works. But then it hits you: the real news is not the building, which is fine. The news is the sequence of jolts as you walk from one room to another and take in SAM's new pieces, the influx of great works from collectors celebrating the building or the museum's 75th anniversary. By one estimate, the 1,000 new pieces are worth more than $1 billion. The quality and range of the additions is extraordinary, from Edward Hopper's "Chop Suey" to John Singleton Copley's "Sylvester Gardiner." I like how it can go from the reverential (first-century Roman marble) to the nutty (a fake dog asleep on a chair).

Of course, the new SAM is yet another reminder that some in Seattle have made a lot of money in the past 20 years. But what do you say about a guy like Jon Shirley, the former Microsoft president, who's donated millions, and he's walking through the galleries, listening to the guides, marveling at the art, smiling, and saying, isn't this great? It is.

Several years ago, the Shirleys, the Brotmans, the Wrights, and many others put SAM on warp drive and unquestionably made our city better: They built a new Sculpture Park and now a new downtown building, crammed with goodies.

How'd we get so lucky?