Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Bewitched, Bothered, and Bewildered
The narrators of The Virgin Suicides have an attitude of obsessive fascination towards the subject of the Lisbon sisters' deaths. They're absolutely enamored of the girls, obsessed with learning everything they can about them. After one boy, Peter Sissen, manages to go into their house, he comes back with awe-inspiring stories:
[…] of bedrooms filled with crumpled panties, of stuffed animals hugged to death by the passion of the girls, of a crucifix draped with a brassiere, of gauzy chambers of canopied beds, and of the effluvia of so many young girls becoming women together in the same cramped space. (1.11)
The tone of the novel has been described as "dreamlike." Because the boys actually know so little, their imaginations run wild. The result is a tone of wonder and fantasy—"gauzy chambers," "the passion of the girls," etc.
There's also a very melancholy tone running through the novel. After all, the subject matter is death and loss. The narrators constantly reach back and try to understand what happens, but the reality of the girls' experience eludes them. In trying to understand the girls, they're trying to bring them back. They never can understand them, so it's a reliving of that loss over and over again. The parents' grief, the sisters' withdrawal—it's sad, sad, sad. There's a general feeling of decay and disintegration. "Ruin and decay" were the atmosphere the author was going for and we'd say he succeeded (source).