The Phoenix Art Museum has been reborn and expanded and broken into the next tier, morphed suddenly into a major cultural institution, now blessedly the right size for sixth largest city in the country.

Whether or not it's a good building - we'll get to that.

Physically there’s more room, new seriousness, a higher-frequency vibe. You would never know by walking past, out on the corner of McDowell and Central where PAM turns its back on pedestrians, but you can feel that vibe immediately in the new lobby. One little problem with the old lobby was nobody could find it. Too subtle. The new lobby registers entrance like a flashing red neon arrow, and I'll meet you there in four paragraphs.

PAM has reincarnated in place four times. The old bones of the Cultural Complex plaza were built in 1959, and most elements of that relaxed mid-Century design by Alden Dow and Blaine Drake are still here. The second layer was Dow and Drake expanding again in 1965. Ten years later the Central Library was enlarged along McDowell, only to be kicked off site, down the street, in 1996 when the museum hired New York architects Tod Williams and Billie Tsien.

This had been the first big commission for Williams / Tsien. (They are married, to each other, and operate from New York. She has the more poetic outlook. He calls himself a 'work beast.') Their first proposal was a calculated splash, a 500-foot-long section of shade-creating elevated highway with massive columns, parallel to Central, which was bold, expensive… and rejected. A later version of the plan for 1996 included a 90-foot-diameter fiberglass sculpture pavilion / cooling tower / lantern / beehive in the central courtyard. The current massing along Central, those two long green sheds with angled rooflines converging to a gap, makes more sense as counterpoint to that phantom beehive. In any case, without the beehive, they expanded PAM to 160,000 square feet.

Now this latest expansion brings the square footage to 203,000. The cost was $41.2 million, and for the expansion PAM sought new architectural blood in the form of…. Tod Williams and Billie Tsien.

Which, for visitors, is great news.

Your next move is a narrow, white passageway, the 'John Morrell Promenade,' a sort of interior canyon where the ceilings vault up to 26 feet and where a high window can be read as homage to James Turrell. Move onward a few feet, and you'll notice the second floor. That's new. In the 1996 building many visitors had strolled in, looked around, happily strolled out, and missed the upstairs completely. (Too subtle.)

From this white canyon, you approach the familiar spaces from a new direction. The old rhythms and spaces of the Asian wing and the Thorne Miniature Rooms and all the rest connect to give you a not-unpleasant rambling feeling, like an old complicated family house that's been added onto multiple times.

But your options are always clear. According to PAM director Jim Ballinger, the prime issue for this renovation was visitor arrival, anticipation, orientation and flow. Unlike other architects whose museums make visitors dizzy enough to fall over backwards (Mr. Liebskind), who compete with the art (Mr. Holl), or whose buildings qualify as emotional abuse (Mr. Eisenman), Williams and Tsien pay careful attention to human scale and user experience. They attend to the inside of the building, and communicate in English words. Obviously they already knew the building, saving a year of effort by Ballinger's reckoning.

And great spaces are less like automobiles delivered finished from the factory, and more like gardens, the product of time, trial and error, corrections and natural growth and benign neglect. In the spirit of Jan Gehl, the Danish urban planner who's been perfecting a chunk of Copenhagen for 35 years, it's right that Williams and Tsien come back and redeem and improve their previous design.

So as you walk through the old lobby and alongside the Great Hall, you're approaching PAM's new heart, the Katz Wing for Modern Art.
There's a moment coming up where you might forget where you are. A new enormous wing proportioned for the museum's contemporary collection, the eye is drawn upward by showpiece staircases, the high ceiling (46 feet), and the 10-foot-deep subtly colored "sky box" overhead. It's a reliably impressive moment, and the museum's new center of gravity.

Only the perimeter walls in the Katz Wing are permanent. The museum judiciously dropped an extra million dollars to create free-span space, flexibly configurable in the middle. This allows the curators to display their modern and contemporary collection, for instance the Donald Judd piece received damaged and stuffed into storage 50 years ago. This space also allows the Great Hall, which now seems like a little brother, to be used for event space, and puts PAM in the running for major exhibitions.

All four levels of the Katz Wing are full of quietly supportive architectural moments. I'll leave you to check out the Fashion Design Gallery, fit comfortably into the configuration, and discover the light well downstairs with the granite reflecting pool, and the comfortable observation alcoves overlooking McDowell to the south and the courtyard to the north, the clever cutouts and segues and wayfinding cues, the control of potentially harsh daylight, and more than anything, the beautifully rhythmic staircases and platforms.

The natural last thing is to stroll into the middle courtyard, the Dorrance Sculpture Garden, perhaps into the café patio area. There’s 150 trees and a new water feature out there, flush with the ground, which some patrons have found tricky. (Too subtle.) At night the garden is peaceful and inviting in the way of an exquisitely manicured back yard.

So is this a good building? Well, from this viewpoint it's clear that Williams and Tsien delivered a brilliant partial addition to a campus, not a complete overhaul.

Look around, and you can see the old leftover shapes of each reincarnation. You have a good view of the 1996 massing and its own complications. These shapes get along, sort of, but don't fit together effortlessly. The garden plantings, in fact, were meant to add cohesion and consistency to this view.

There are some mid-Century relics visible - that line of distinctive grey 1959 columns, and the Phoenix Theatre sign in a font floating up from civic memory - and I hope that somebody at PAM appreciates those signals as much as I do.
The experience of PAM contains PAM's own history, which is kind of wonderful. It's more like a garden than a car.