Whitechapel Reopening, Whitechapel Gallery, London

But there has been another, coexistent Whitechapel – a place of national interest, that introduced Jackson Pollock to Britain (1958), first showed Pop Art in London (1956) and hosted Picasso’s Guernica on its world tour (1939). One of the gallery’s directors (Nicholas Serota) went on to run Tate Modern, and another (Iwona Blazwick, the current incumbent) seems likely to follow him. Like no other art space I can think of, the Whitechapel has juggled local and national roles. So what now?

This is an exhibition review, so I won’t blah on about the gallery’s expanded building, other than to say that it is elegant, ingenious and that many of its nicest spaces have been given over to education. To all of which, I think, we say hurrah. Its opening show (or shows, these being multiple) will be scanned for future intent and there, too, we can clap our hands.

In the main galleries is Open, Sesame!, a retrospective of the work of Isa Genzken, a German artist better known elsewhere. Neatly for an institution whose role is both historical and contemporary, the Whitechapel has divided Genzken in two. Her work pre-1999 is downstairs and post-1999 upstairs, the disjunction between these being so marked as to shock.

Twentieth-century Genzken raised a cool eyebrow at the aesthetics of Minimalism, putting TV bunny ears on concrete blocks or turning them into loudspeakers. Carl André would not have approved. The work, though, wasn’t just jokey. Paintings such as

MLR(1992) reinvented the Modernist grid as something brooding and sexy, like Agnes Martin on Viagra. I’ll confess to disliking boy-art, the kind made from formulas and The Ladybird Book of Science. But there

Ladybird Book of Science. But there is an equally tiresome girl-art, cod analytic, petit Bourgeois, on message – or rather, Messager; and that, unexpectedly, is what we find upstairs in this show. Starting with a series of works called Fuck the Bauhaus – given the history of Germany in the 1930s, an unusual choice of name – 21st-century Genzken turns her back on Minimalism and goes instead for Maximalism: pizza boxes, ribbon, flowers, Dinky toys, shop dummies. There’s a story being told here, but who can be bothered to read it? Not me.

Were it not for the context, this might be irksome, but there are all kinds of befores and afters going on at the new Whitechapel, and Genzken’s is merely one of them. In a smaller space downstairs, the Turner-Prize-listed Goshka Macuga rewrites the gallery’s own history courtesy of Guernica, lent for the occasion by its American owners. It is 70 years since the image last hung here, and both it and its meaning have changed with time.

This is not, of course, the real Guernica – that is too fragile to leave Madrid – but a Picasso-approved tapestry copy, normally hung outside the United Nations Security Council in New York. This was notoriously curtained over when Colin Powell addressed the council on Iraq’s weapons of mass destruction, US television deeming the work too disturbing a backdrop. The irony of this, as of the dual meanings of the words “coverup”, has not been lost on Macuga, who brings Guernica back to slippery life in a debating chamber of her own.

Two other rooms also look back to the new gallery’s future. In its archive space are works by the Whitechapel Boys, an early 20th-century group centred around David Bomberg and Mark Gertler. Near this are star buys from the British Council Collection, including everything from an early Henry Moore to an early Anish Kapoor.The story these rooms tell is the history of the Whitechapel – of a consistent championing of the avantgarde, a courageous integration of the new, difficult and foreign; an openness to names such as Bomberg and Kapoor and, now, Genzken and Macuga. It’s always worrying when an old friend has a facelift, but there’s no need for anxiety here. The Whitechapel is what it has always been, and that is utterly admirable.

WhitechapelGallery, London E1 (020-7552 7888) from today