There was a bit of a Woodstock reunion feel to the Mostly Mozart concert at Avery Fisher Hall Thursday evening as threefourths of the Emerson String Quartet, two-thirds of the KLR Trio and the one and only Leon Fleisher got together for a convivial night of chamber music. Since the Emersonians were calling the shots, the players, except for the cellos, stood for most of the recital. Although it is undoubtedly true that the popular quartet was in need of some retooling a couple of seasons ago, their debatable decision to play upright going forward has done little to increase their overall musicality.

The program began with a rather cold, but occasionally elegant String Trio in G by Beethoven.This early work is only a step above tafelmusik and needs a bright, ebullient reading to keep it interesting. Instead, we were offered a pedestrian, albeit accurate, rendition, which really only reached the heights of grace during the nimble Scherzo. With Emerson violist Lawrence Dutton on the disabled list with a rotator cuff injury, veteran violinist Jaime Laredo switched instruments to join in.

Leon Fleisher can certainly relate to Mr. Dutton’s recent infirmities, as he spent many years out of the limelight after carpal tunnel injuries to his right hand. After years of rolfing therapy, Mr. Fleisher is now back concertizing, and that is a good thing. He joined Eugene Drucker and Philip Setzer, violins, and David Finckel, cello, from the Emerson group as well as Richard O’Neill, viola, and Timothy Cobb, bass, in a salon arrangement of Mozart’s Piano Concerto No. 12.

Wolfgang opened the door for this type of reduction by stating that the piece could be performed in any number of combinations. By now, it has probably been arranged for every instrument from accordion to zither, but this particular setting seemed to work fine. It is a joy to report that Mr. Fleisher performed admirably, though this was competent playing, nothing more. There was not a great deal of delicacy or singing line, but there was a good sense of architecture and a steady touch. You have to admire the ingenuity of the man, making adjustments to compensate for his physical condition — for example, using his entire hand mechanics in constructing a trill rather than relying on the uniform dexterity of individual digits. Just seeing him up there was miraculously inspirational.

I realize that I am in the minority here, what with their winning 100 Grammy awards in a row and all, but I have always found the Emerson Quartet lacking a certain je ne sais quoi perhaps best described in musical terms as soul. They could make early Beethoven and Mozart accompaniment work, but once the subject was Brahms, they sounded woefully deficient. Joined by Messrs. Laredo and O’Neill, and Sharon Robinson, the cellist of KLR, their realization of the Second Sextet was far from the quivering, passionate expression of young love that the composer intended. With this level of intensity, just presenting the notes on the page is hardly enough. And, to make matters just a tad less interesting, they ambled along at a snail’s pace, the final movement too much Poco and not enough Allegro.

It has been a long time since I have seen someone exit the hall from a stage seat, but this night a woman arose during the Brahms Scherzo, sidled past all of her neighbors in her row, walked all the way down to where she could practically touch the backs of the musicians and made her way to the exit. Everyone in the audience observed this and at least one of us, by this point, was wishing that he could go with her.

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Would the Mostly Mozart Festival end with a bang or a whimper? With no contemporary pieces or soloists to hide behind, the summer orchestra and its conductor Louis Langrée opted for a difficult final program, a Mozartian acid test. This season had exposed the soft underbelly of the group, a discernible dip in discipline and crispness. How would it fare as interpreters of the last three symphonies?

In the main, quite well, although initially it did not appear that the evening would be a success. The very first note of the Symphony No. 39 was struck in a scattershot manner, the timpani, which plays a key role in this opening, martial Adagio, perceptibly behind. But those who are familiar with this great work, somewhat overshadowed by its two successors, know that it is much more important to close well than to open as a unit. The very tricky final phrases of the fourth movement Allegro were not only nimble and precise, enunciated against a complex background of pauses, but concluded a brisk and mostly muscular performance. The lilt in the Menuetto was appropriately Viennese, a foreshadowing of those delightful skater’s waltzes in the works of Franz Schubert.

When asked to name the greatest 10 symphonies in music history, most everyone includes the Mozart 40 in their listing. Mr. Langrée hears it at a fast pace and whipped his charges to faster and faster execution as they progressed. This was the finest performance of the evening, featuring a lean and mean sense of phrasing and a delicious bite of wishing to get on with it. No lingering in this rendition, where even the minuet seemed to emphasize exits rather than entrances. The final Allegro assai was taken at such an alarming alacrity that I anticipated the double basses, who have two key reprises of melody, would never posses the dexterity to enunciate clearly. However, they came through with flying colors , earning a fleeting, but welldeserved thumbs-up gesture from Maestro as he hurried on to the next section.

So, not to rain on their parade or anything, but the question quickly evolved to why this particular iteration of the white-jacketed band could perform so well in their swan song and yet so sloppily in previous concerts. My own theory has little to do with inspiration or perspiration, but rather, rehearsal time. Mr. Langrée spread himself quite thin in the earlier stages of the festival, spending considerable energies mounting what turned out to be a disappointing evening of bleeding chunks of the fragment “Zaide” with incidental music from Thamos, King of Egypt. Working with the period instrument folks from Cologne had to monopolize a significant amount of his preparatory time and it can’t just be a fortuitous coincidence that once he was unburdened of this quixotic project, his main ensemble began to gel. The festival, struggling for relevance in a Mozart anniversary year, might have forgotten that the key to lasting success is not trendiness, but quality. It is fine to program rare works with glitzy names, like Peter Sellars, but it is much more musically significant to present the core repertoire in as professional a manner as possible.

In the same week that Pluto was demoted from its status as a planet, the “Jupiter” — the Symphony No. 41 in C major — was perhaps not as grandiloquently encased in marble as it might have been, but was still offered as a model of Classical architecture and timeless grace. I would posit that this is as good as it gets for this essentially ragtag ensemble. It was unfortunate that it did not find its proper balance and battle-hardened voice until the last concert of the season, but hey, wait ’till next year.