OPERA / Unfaithful with the original: Robert Maycock on English Touring Opera's Cosi fan tutte and Falstaff, stopping over at Sadler's Wells

The usual wisdom about Cosi fan tutte has it that the men are beasts and the women, on whom they test their theories about fidelity, are pathetic victims. Mozart started it by giving the women music that breaks your heart along with theirs. But suppose the men are just behaving the way you ought to expect, and Fiordiligi and Dorabella are fools to trust them? Clare Venables' new production sends up their romantic illusions something rotten. She introduces the sisters as art students in love with, respectively, a Che Guevara lookalike and a model for shapeless sweaters. In the garden scene they mope around in scruffy dressing-gowns, consoling themselves with chocolate cake. They don't deserve your sympathy but they still get it; and the combination of a clear eye and a generous heart, theatrical freshness and musical sensitivity, is what gives this English Touring Opera staging its special character.

Beneath all the games, the story is about misplaced trust and undermined certainties. The innocent, naturalistic settings gradually become surreal. Ferrando and Guglielmo go off to war in out-of-period uniforms, and return disguised in luminous pink and green business suits - a neat dig at our expectations of exotic strangers. Despina, at first the standard Glaswegian maid, teaches a sharp line in art history, with special scorn reserved for Manet's Olympia. The opera's world careers on with a pantomime logic of its own, and at the end its neat symmetries can no longer be restored.

In that, it cannot help recalling the classic Cos production of recent times, David Freeman's for Opera Factory. With ETO the tone is more amused, the descent from farce to despair less steep. But it's truer to the ambivalence of Mozart's music. For the famous 'farewell' sequence of quintet and trio, Venables counterpoints images of cynical detachment and genuine loss, just like the score: simple gestures with a sequence of shrinking handkerchiefs, at once absurd and touching, catch the mood perfectly. Even Alfonso, the plot's arch- manipulator, is moved by his own acting.

Ivor Bolton, conducting his final production as the company's music director, keeps the pace brisk, the manner tense and elegant, with a couple of glorious, sensuous expansions - notably for Fiordiligi's second-act aria, which Catherine Pierard sings with tenderness and, later, spirited flair. Andrew Burden, as Ferrando, also beguiled the ear in Monday's opening performance, but the whole vocal ensemble is well matched and balanced and the musical experience adds up to something for the staging to be worthy of.

When ETO was Opera 80 it would often pair an exploratory, unsettling production with a direct and uncomplicated one, and this season Verdi's Falstaff carries on the tradition in Tim Hopkins' lively staging, revived at Sadler's Wells on Tuesday. Not that it lacks sophistication: the stage movement is deft and inventive, mixing commedia dell'arte stylisation with robust English humour, and Peter J Davison's sets range from a Garter Inn like the Hayward Gallery on a wet day to an expressionist Windsor Forest in brilliant green and yellow cut-out.

Falstaff himself is as everybody loves to imagine him, debauched and avuncular with a glint in the eye, and taken by Jonathan Veira with a fine line in mellow lyricism as well as the bark that is worse than the bite, and a presence that easily dominates. Strong singing too from Patrick Donnelly's Ford, flaunting the magnificent outrage of the bourgeoisie, and Margaret Preece's quick-witted Alice. Falstaff, a musicians' opera before all else, depends more than most on the orchestra's delight and relish, and Charles Peebles conducts with a light hand that lets them make the most of it.

Last London performances: 'Cosi fan tutte' tonight, 'Falstaff' tomorrow, Sadler's Wells, London EC1 (071-278 8916). Then tours: details on 071-820 1131