While Delaney is a science-fiction writer, this is not really a science fiction book. It is magical realism if it is anything and the book is profoundly experimental. It doesn't have a plot that you can summarize, but essentially a person known only as The Kid arrives in a city in which a disaster has happened and is now inhabited only by the insane and counter-culture types. There he writes poetry, has a lot of sex and becomes a gang leader. That actually makes the book seem much less strange than it is.
Dhalgren if it is about anything is about the counter-culture of the 60s and 70s. I don't know if it means anything, but it is written with precision. It is also very long. While not much violent happens in the book it seems infused with violence. It also has a kind of dream logic to the writing. Its technically well done, but I found myself ground down by it and I had to force myself to read it. Its interesting, my guess is it will turn out to be memorable, but I found it grueling and I have a high tolerance for this kind of thing.