Has the Philadelphia Orchestra ever had a fun music director?

The closest contender was Simon Rattle - until the spirited Yannick Nézet-Séguin, who seems to be having a grand time hopping around the globe and is promising to alight, with a hoped-for degree of permanence, upon the Philadelphia Orchestra.

Levity has never been a priority in the serious world of classical music. We're talking about a musical CEO - and huge responsibilities to deliver world-class Beethoven, Brahms, and Mahler.

So here's a conductor who seems to have a perpetual air of celebration. Well, perhaps during this dark time in the Philadelphia Orchestra's history - and when the classical world is more concerned than ever about extinction - grim determination isn't the route to survival.

That's one explanation why the exuberant Gustavo Dudamel is the world's hottest conducting talent, with Nézet-Séguin not far behind, according to well-placed music industry sources. Both can be reckless, all but inviting backlash. Neither is a paragon of consistent musical maturity. But they offer a legitimate sense of renewal, which may be as much a matter of image as substance, at least from a fund-raising standpoint.

I felt thoroughly renewed by the Mahler Symphony No. 3 led by chief conductor Charles Dutoit last week. The only drawback of Dutoit, 73, is familiarity - though we can hope he'll maintain a significant role with the orchestra for years to come.

Musically, I find Nézet-Séguin hugely engaging and often enlightening. His broad-reaching repertoire is essential for any resident music director. Monitoring his unedited radio broadcasts, I've heard perhaps the single greatest performance of Gershwin's Piano Concerto in F and, at the other end of the depth scale, a Mahler Symphony No. 9 that went as far into that music's abyss as any of Nézet-Séguin's great predecessors.

Between those two poles, matters get iffy. A Beethoven Symphony No. 3 from Rotterdam a few years ago was full of strong ideas that didn't entirely belong in the same performance. Sometimes I wonder how well he knows his own strengths. Though his Franck Symphony in D minor performance in Philadelphia was hardly one for the ages, few performances I've ever heard of this questionable piece are worth remembering.

Nézet-Séguin is an extraordinary accompanist. The veteran Aldo Ciccolini compares him to the late Carlos Kleiber (the great, reclusive German conductor). Praise doesn't get any higher. His Rachmaninoff Piano Concerto No. 2 with Andre Watts brought out poetic depths in that pianist I never knew existed. He also indulged Nicholas Angelich to play an ultraslow Brahms Piano Concerto No. 2. Let's hope he learned from that mistake.

I've often felt that Philadelphia Orchestra music directors should only be people with nothing to lose - and in years past Wolfgang Sawallisch fit that mold perfectly, coming to Philadelphia after a long career. It was icing on a cake that didn't need any.

But in an indication of how times change, Nézet-Séguin also has nothing to lose, for completely different reasons: So many people want a piece of him that if Philadelphia doesn't work out, any number of other orchestras will happily grab him.

In some ways, Philadelphia's situation is parallel to the New York Philharmonic's in the 1950s: With the old-world, Sawallisch-like Bruno Walter in semiretirement, Christoph Eschenbach-ish Dimitri Mitropoulos' having met a hard-to-explain Waterloo, and financial problems everywhere, the orchestra was in dire need of Leonard Bernstein. No matter that he was gray-listed during the McCarthy era and exiled from that orchestra for five years. He promised renewal - and delivered it, for audiences, though critics often found him too showy and his interpretations too green. Sound familiar?

In light of other precedents, Nézet-Séguin looks even better. He is far from being an Eiji Oue, who landed the Minnesota Orchestra (1995-2002) but, for all his youthful charm, was in so far over his head artistically that he seemed to be on the way out from the year that he arrived.

Nor is this a reprise of Mstislav Rostropovich's National Symphony Orchestra tenure, which stayed afloat thanks to some spectacular specialties but, in other areas, had him learning on the job - not well or quickly - throughout the 1980s.

In fact, I have only one reservation about Nézet-Séguin: His tenure begins too gradually. That's downright dangerous, given how quickly a guest conductor can steal an orchestra's affections. That was partly the basis of Jean Martinon's unsuccessful tenure with the Chicago Symphony Orchestra (1963-68). And from what I can tell, he had the potential to be as great as anybody.

Contact music critic David Patrick Stearns at dstearns@philly.com.