Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Mostly Tragic, Some Comic
In "The Silent Towns" we get a comic version of the "last man on Earth" story, with Walter Gripp learning to be happy alone instead of living with a hideous woman who makes the mistake of eating chocolate in front of him. By comic here we mean both that it's a) funny(ish) and b) has a happy ending. (And for Gripp, being the last man on Mars is a perfectly happy ending.)
But in "The Long Years," Bradbury writes a tragic (and kind of creepy) version of the "last man" story, with Hathaway building a robotic family to replace his original one. Gripp may gain something (peace and solitude), but Hathaway's loss somehow seems a lot more likely.
This alternation between comic and tragic is all over The Martian Chronicles. Like, in "Ylla," Yll says that Earth could never support life because "Our scientists have said there's far too much oxygen in their atmosphere" (43). That's comic because it's dead wrong—it's oxygen that makes life possible on Earth.
But keep in mind that Yll makes this comic remark in the context of a loveless marriage that will soon lead him to murder. So, you know, tragic for Ylla, who's suffocating because of a lack of oxygen—we mean, love.
In the end, you're not going to have to use too many fingers or toes to count up the funny moments, because, really, the stories are mostly tragic. After all, the humans wipe out almost all of Mars and then blow themselves up in nuclear war. Not exactly a laugh riot.