Thematic art exhibitions can be fascinating because, if the curators have done their research well, you get to see some interesting but unknown works. The downside is that at the periphery of the exhibition you often find works that make you wonder why on earth they have been included and which obscure rather than illustrate the exhibition's theme.

At "Faces in the Crowd. Picturing Modern Life from Manet to Today", an ambitious exhibition at London's Whitechapel Art Gallery, I was delighted to see Sophie Calle's "Suite Vénitienne" (1980) alongside Francis Alys "Doppelgänger" (1999) and a work by the American artist Vito Acconci from 1969 whom I had never heard of before. Acconci picked out a random person walking in the street and followed that person until he or she disappeared where he could no longer follow him or her. It is therefore very similar to Sophie Calle's "Suite Vénitienne", which documents her following a man she met on the streets of Venice. Francis Alys' "Doppelgänger" is a record of his advice to travellers arriving in a foreign city to wander around searching for a person looking like yourself and to then walk beside that person until your pace adjusts to his or hers. I had read about Sophie Calle's "Suite Vénitienne", although I don't recall ever actually seeing it and so it was interesting to see it side by side with the similar projects by Francis Alys and Vito Acconci.

On the other hand I wondered what Francis Bacon was doing in this exhibition and why one of the last works in the exhibition was a painting by Chris Ofili. And what is that video of one of Paul McCarthy's performances from the early 70s doing here? And why was the portrait of "Maika" (1929) by Christian Schad selected as the cover for the exhibition flyer? I'm afraid I'm missing something here.

There seem to be two main threads in the exhibition. One focuses on the representation of crowds and gatherings and runs from Manet's "Masked Ball at the Opera" (1873) and cafe scenes by George Grosz and Max Beckmann to Andreas Gursky's photo of a rave party, "May Day II" (1998). Another somewhat looser thread connects works representing the individual in the crowd, from the anonymous to the celebrity and from Gerhard Richter's portraits of eight student nurses (1966) to Andy Warhol's "Jackie" (1964) after a snapshot of Jacqueline Kennedy.

In between there was an intriguing series of three photos by Richard Prince from 1978 of a man in a suit looking in different directions in a street, in front of a yacht and what maybe a restaurant. There was a video by Steve McQueen of two black men walking through London each carrying a palm tree and a video by Gilliam Wearing of a girl dancing in a shopping mall. There were photos by Brassai and a silent movie of street scenes by Dziga Vertov from 1929 alongside a video of Shanghai by Song Dong from 2000.

There was too much as a matter of fact, but in a way there was also too little. If this exhibition had been organized by the Centre Pompidou in Paris, it would have been three times as big, covering an entire floor and at half the price.

Unfortunately, the architecture of the Whitechapel Art Gallery also imposes a linear parcours when I would have liked to be able to go from Raghnbir Singh's photos from Bombay back to René Burri's photos from Sao Paulo (1960) and Helen Levitt's New York City street scenes from the 1940s, without having to descend the stairs. Still, there is much to see and enjoy at this exhibition. There's work by Jeff Wall and Gilbert and George and there are some of Cindy Sherman's "Untitled Film Stills" and Walker Evans subway portraits. If you've got time, which I hadn't, you can sit down to watch Chantal Akerman's slow but poetic "D'Est" (1993). I also enjoyed seeing Bruce Nauman's "Clown Torture" again, especially after having heard the soundtrack at the Tate Modern, even though I wondered why it had been included.

Faces in the Crowd is at the Whitechapel Art Gallery, London until 6 March 2005.