I can't speak to Jim Carroll's abilities as a punk musician -- all I know is that he wasn't as good as the Ramones, but then who was -- but I do remember The Basketball Diaries as a huge hit when it appeared in the late 1970's. It was witty, easy to read, called up slumbering Beatnik memories which by then had seemed extinguished, and the story was certainly realistic enough to anyone who had spent time in NYC in the 1960's. The city at the time was a haven for young runaways who had grown up absurd elsewhere in America, and many of their stories were simply amazing--Holden Caulfield would have appeared like a dork in comparison with these kids, many of whom seemed to have either gone feral or else were still searching for a different planet to live on.
Jim was promoted by Ted Berrigan and hailed as a brilliant young writer, and royalties from the DiCaprio film in early 90's must have felt good, but unfortunately the Diaries were never followed by a second book as good as the first. Not a big surprise--I can't think of a single novelist in the adolescent enfant-terrible genre that ever achieved further success except Mark Twain, and so they have remained one-book authors.