Soirée Rossiniana, Barbican Hall, London<br>Monteverdi Choir/ English Baroque Soloists, Christ Church, Spitalfields, London<br>London Philharmonic, Royal Festival Hall, London

Take one packed venue, add a fistful of diamonds, two impressively cantilevered evening gowns, a self-effacing pianist, and one of the most maddening and beguiling voices in the world.

Had Soirée Rossiniana been a gentle stroll through familiar operatic arias, few would have complained. But Cecilia Bartoli's artfully dovetailed programme of French, Italian and Spanish songs by Rossini, Bellini, Donizetti, Pauline Viardot, Manuel del Pópulo Vicente García and his famous daughter Maria Malibran offered a series of delicate miniatures on melancholy, dreams, water and love.

Bartoli makes her peers seem lazy. Too musicologically minded to fit the stereotype of an international diva, too curvacious to play the great mezzo trouser-roles, too small a voice to escape the baroque and bel canto niche, she seems happiest in recital. Free from the hassle of props, costumes, conductors and producers, she can create and control her own worlds, from the crowded waterfront of La regata veneziana, the limpid gardens of L'Abbandono and the peacock-feathered love-nest of Me voglio fà'na casa to the lawless freedom of El Poeta, and the tongue-in-cheek military zeal of Rataplan.

Her technical idiosyncrasies remain bewildering. Eyebrows and mouth work overtime in coloratura passages, trills are bizarrely aspirated and curdled, the tone is squeezed and blanched, the chin tucked in. But Bartoli's soft-spun top notes and silken portamenti are so exquisite that you want to blow her a kiss. Potentially as mawkish as a Country and Western ballad, Rossini's L'Orpheline du Tyrol – in which a half-frozen orphan yodels in remembrance of her mother – was as touching as the wistful Ariette à l'ancienne. In Donizetti's Amore e morte Bartoli's graceful phrasing made me long for a more expressive accompanist than Sergio Ciomei. The swaying rhythms of Viardot's Havanaise hinted at the sensuality of the encores, Ernesto de Curtis's Non ti scordar di me and Ti voglio tanto bene. An imaginative and unfailingly sincere performance.

On Monday, John Eliot Gardiner, the Monteverdi Choir and the English Baroque Soloists gave the first of a six-concert series of motets, Brandenburg Concertos and cantatas from the Christmas Oratorio at Christ Church Spitalfields. With 30 singers, two cellos, a double bass and two organs, Gardiner's reading of the double-choir motet Komm, Jesu, Komm was more decorous than I would ordinarily favour. The steam-ironed repetitions of "Ich sehne mich" and broad rallentando on "Der saure Weg wird mir zu schwer" were almost Mendelssohnian, while the final chorale's long crescendo flirted with vulgarity. This was Bach driven like a Mercedes limousine. The sixth Brandenburg Concerto came from another aesthetic; something lighter, more intimate and improvisatory. The cantata Jauchzet, frohlocket sparkled, with some cheeky countermelodies from harpsichordist Ivan Moody, vivacious flutes and violins, a flawless trumpet solo from Neil Brough, and a tender alto solo from Clare Wilkinson. The series resumes on 5 January.

Vladimir Jurowski seems more interested in encouraging individual expression than Gardiner, but he too favours extreme tempi and meticulously engineered dynamics. The London Philharmonic Orchestra's concert performance of Act II of Tristan und Isolde set off at a rocketing speed, lending urgency to the dialogue between Isolde (the wonderful Anja Kampe) and Brangäne (Sarah Connolly), and emphasising the sublime stillness before the ecstatic duet with Tristan (Robert Dean Smith). Balance between voices and orchestra continues to be problematic in the Royal Festival Hall, though Connolly's watchful soliloquy from the organ loft was ravishing and Jurowski was sensitive in his support of the flu-stricken László Polgár (King Marke). While the strings lacked lustre, the fluttering woodwind figures were beautifully delineated.