I'm sort of surprised at how much Ballard I've ended up reading this past year or so. I always had a negative feeling towards him. Not based on anything substantial but just because his name came to me surrounded by all that "alternative" hype when ReSearch published The Atrocity Exhibit and Crash the movie came out (which I kind of enjoyed). Now I've read enough of his early work to feel that I have a decent handle on his style and some of the themes he deals with.
Concrete Island is the story of a succesful London architect who loses control on the freeway and drives his Jaguar over the edge, crashing in an isolated island underneath a huge interchange. He is mildly injured and in a bit of shock (or perhaps insane; it's often hard to tell with Ballard's characters) but it's not a big deal until he tries to get off of the island. It turns out that he's trapped. There's no obvious way out and on the only road he can reach, the motorists are driving too fast and won't stop. He acts a bit rashly, makes some mistakes and ends up looking pretty disheveled, which makes people even less likely to stop.
It is of course a metaphor for the isolated modern man as well as a condemnation of society's separation (or, considering Ballard's morally neutral tone, a confirmation of man's nature). The storyline does get more complex, but ultimately he's addressing many of the same themes he deals with in his first four apocalypse novels: man's psychological distance from civilization, the flimsiness of bourgeois trappings, etc.
It's a quick read, very dark, even cruel at times. His description of the island (it's fairly complex, being the remains of an old neighborhood) is excellent. It's a small study and engaging, but it will not make you very happy.