FEW OPERAS haven't, at some time, suffered the charge of "Lovely music, shame about the plot". "Ludicrous" and "illogical" are two of the epithets which are hurled at the libretto of Weber's Oberon, written for Covent Garden in 1826. Librettist James Robertson Planche (the name itself a glorious hybrid) takes the blame. In the programme for Richard Hickox's concert performance at the Barbican on Thursday, the Weber expert John Warrack writes: "It would be difficult now to stage an 'authentic' version, with all Planche's involuted and fanciful language, his unnecessary sub-plots involving non-singers, his pages of material intended only to provide for the designer and the producer and the stage technicians." Which sounds a fairly modern conception of total theatre, or it might make a good Disney cartoon (as long as Elton John didn't rewrite the music).

Hickox's performance (the second of his three evenings related to A Midsummer Night's Dream; Britten's Dream is on next Tuesday) made a case for Oberon in concert, but not wholly convincingly. To link musical passages, Warrack provided a narration, read by Timothy West. But it was hard to follow the plot, and the singers, unsurprisingly, simply stood and delivered. As a result, theatrical magic erupted only intermittently.

Hickox really knows his orchestra, the City of London Sinfonia, and it responds well to him. And there were moments of beauty, beginning with the opening sound, a horn that echoed throughout the opera (and the 19th century, eventually becoming Mahler's Wunderhorn). The London Symphony Chorus was on song, but it's the solo voices that make or break. And the women shone: Susan Gritton in a lovely cameo as a Mermaid, hovering high above the chorus; and Jean Rigby as a rather elegant Puck.

The only part of Oberon that has had a genuine afterlife is Reiza's magnificent Scene and Aria, "Ocean! Thou mighty monster," an opera in miniature, through which Christine Brewer, as yet no Jessye Norman, marshalled her resources carefully, riding the surging musical waves with grace. The voice thins a little under pressure, and this is music that knows how to apply pressure. But Brewer's charismatic performance lifted the evening to a plane from which magic might happen.

Eighteenth-century opera seria used to be lingua incognita for contemporary audiences. But over the last two decades, we have began to understand its strange, highly decorated inflections. London audiences over the past few months have enjoyed a seria glut, with English National Opera and the Royal Opera staging Handel, and two of Mozart essays in the idiom from Welsh National Opera and Opera for Europe. Now, yet more Handel as, last Tuesday, the London Handel Festival opened with a production of Radamisto in collaboration with the London Royal Schools' Vocal Faculty.

This, the first opera Handel wrote for the Royal Academy of Music, was presented, the programme revealed, in its original 1720 version (minus dances), the first staged revival of the opera in that form. It was quaintly authentic to provide a word-book with the Italian libretto and Anthony Hicks's translation, but rather less authentic to dim the lights so that we couldn't read it. Of course, you shouldn't need printed text to find out what's afoot in a staged performance, but Robert Chevara's production was grimly undemonstrative, giving its young cast precious little guidance as to how to use the space, or their bodies, to provide a context for the music. There was only a generalised sense of who were the good guys, and who loved whom.

Detractors say that's all you need in a Handel opera, but that's no longer good enough: these characters spend so much time telling us how they feel for a reason. To be sure, economics preclude surtitles in the Royal College of Music's bijou Britten Theatre, and no doubt it's good for young singers to tackle Italian. On the other hand, it's also good to learn how to communicate with an audience, and if the budget meant that the production would make a shoestring look glitzy, that's no excuse for silly stagecraft that, for example, forced the villain, Tiridate, to run about like a headless chicken, inducing titters where none were intended.

That isn't a criticism of the singing. I saw the second cast, with Darren Abrahams as Tiridate, and he proved a pleasing singer, the voice never tensing, always shaping the line expressively. As his wronged wife Polissena, Rebecca Watson was superb in the death-defying aria "Sposo ingrato" (Ungrateful husband), at one moment in a tempest of rage, the next floating the note at the limit of audibility. Most moving of all was the Latvian Inga Kalna in the title role, a mezzo-soprano rich in both timbre and promise. On the opening night, the opera was conducted by the Handel Festival's founder, Denys Dadow; on Wednesday, the baton passed to Michael Rosewell, who got a pleasingly rough edge from the London Handel Orchestra. The Festival has plenty more Handel to offer, but, perhaps wisely, is sticking to works that don't need staging.

Reviews habitually describe this or that performance as "revelatory", but at last Sunday's LSO concert at the Barbican, a revelation came which was truly shocking. In a speech accepting the Royal Philharmonic Society's Gold Medal, Pierre Boulez confessed that, about to conduct a Haydn symphony for his London debut in the 1960s, he suffered "10 seconds of complete panic" when he saw a bust of Beethoven. His mind emptied of Haydn's music, and filled instead with Beethoven's Ninth. Panic? Pierre Boulez? Say it ain't so. These days, he resembles the mayor of some provincial French town, proudly showing the best his commune has to offer; which is what he proceeded to do with the LSO in a concert celebrating the 90th birthday year of Elliott Carter.

The only Carter on offer was the Symphony of Three Orchestras, a formidable piece which Boulez made both logical and exciting. It opens with strings performing what may be an imitation of seagulls wheeling around the Statue of Liberty, before a trumpet enters. On this occasion, its brief statement had an aching beauty, like a jazz solo heard through a Greenwich Village window in a Fifties movie. As the orchestral storm began to build, Boulez ensured that conflict, a necessary element of Carter's soundworld, never degenerated into confusion. He is a master of making every gesture count.

In Schoenberg's Piano Concerto, some of the piano's gestures necessarily go for nothing. The orchestral fabric is so densely woven that the soloist sometimes disappears, only to struggle back to the surface moments later. Some see this as a fault, but with a pianist as forthright as Emanuel Ax, it becomes a dramatic detail in a battle for survival against the odds. Boulez and Ax are probably temperamental opposites, the one rigorously analytical, the other impetuous; but Schoenberg himself wrote that "everything of supreme value in art must show heart as well as brain". Here, opposites proved to have an elective affinity.

Boulez received his Gold Medal from Alfred Brendel, who, two days later, himself received a bottle of 1948 Armagnac after his Royal Festival Hall recital, which celebrated 50 years as a concert pianist. Fifty years: the figure is staggering and inspiring, especially in the light of a performance as lithe as this. Articulation in the opening Mozart Fantasy was not always clean, but thereafter, in late sonatas by Schubert, Mozart and Haydn, Brendel was on form, finding a high-stepping swagger for Mozart's opening Allegro and infusing Haydn's syncopations with a tripping delicacy. And it's instructive to remember how much Brendel has done to get Schoenberg's Piano Concerto into the repertoire. He remains a player who takes risks, not in any showily virtuosic way, but as a statement of plain faith in the work. The standing ovation marked not only a fine performance, but a profoundly honourable career.

London Handel Festival (0181 336 0990), to 3 May.