'Ballad' is the word, because that's exactly what it reads like - albeit in prose. The main characters are so oddball as to seem semi-legendary, and the story feels like one that has been lovingly handed down (and no doubt improved upon) through many generations. Successfully sustaining this tone throughout is no mean feat, on top of which McCullers contrives to say more about life and love in 85 pages than many other (good) writers can manage in 500. 'Sad Cafe' really is quite a wonderful piece of literary art.
The seven short stories which accompany it are excellent, too - particularly 'Wunderkind' and 'The Sojourner', which deal very poignantly with two very different kinds of acute disappointment and regret. The only one I thought relatively weak was 'The Jockey'.