Can Darcey Bussell really be leaving The Royal Ballet? Anyone who saw her out-dazzle Carlos Acosta at Covent Garden a couple of weeks ago will struggle to believe she is going. Bussell looks so young and so fresh, and it only seems like five minutes ago that she got here and beguiled us with those legs, that leap, and that smile.

Actually, it isn't five minutes but 20 years since Bussell joined Covent Garden. Since then, the London-born ballerina has won us all over, if not with her acting, which, if we're honest, was only ever average, but with dancing so clear and true that the world briefly seemed a place of harmony, grace and order. "There'll be no comeback," 38-year-old Bussell says in one of the video clips in her sell-out "farewell" show at Sadler's Wells. "No guest appearances."

Instead we have Bussell exiting at her peak, with a final performance at Covent Garden on 8 June, and this whistle-stop retrospective of her career organised by old Royal Ballet chums Michael Nunn and William Trevitt (aka the Ballet Boyz). As we have come to expect from the larky duo, there are handicam interviews, vintage film clips, chit-chat, laughs and a generally unplugged approach interspersed with live dancing.

Not everyone will think this sufficiently respectful for a ballerina of Bussell's stature, but the real problem is that it eats into valuable dance time. At just two hours including an interval, there's only space for six short ballets, a tiny number when you consider the dozens Bussell has danced. Not including a Sleeping Beauty extract, or a Balanchine ballet, feel especially big gaps. However, Nunn and Trevitt do get our questions answered (why is she going? will she come back? what are her plans?)

We also see Bussell as a beaming parent, and then in unexpectedly candid conversation. When asked what she'll miss about The Royal Ballet, she does not say the music or the dancing, but being the centre of attention. "Performers thrive on it," she smiles.

And what of her dancing? Bussell is as crisp and as strong as ever, and her range is considerable. In William Forsythe's In The Middle, Somewhat Elevated she's a sleek Amazon, then all sweetness and light in Frederick Ashton's Cinderella. And in Kenneth MacMillan's Winter Dreams she catches the desperate loneliness of a dutiful marriage, with Jonathan Cope as her luckless husband and Roberto Bolle as the man she loves.

It's unnerving to think MacMillan made Winter Dreams for Bussell way back in 1990. As she turns and spins in the ballet's final "farewell" duet, it's not only her going that moves us, but knowing that our time is also ticking away.

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