A psychologist kills his patients and then himself ("The Earth Men"); the Third Expedition is ambushed; Wilder ends up killing Spender; Parkhill doesn't get his hot dog stand; the Martian dies when he tries to make everyone happy ("The Martian"); and Ylla is stuck in a loveless marriage. Let's face it: most of the stories in The Martian Chronicles end sadly. Even the last one, "The Million-Year Picnic," has a big helping of sadness mixed in with its hope (the end of the Earth is kind of sad, we guess). Even though Bradbury is talking about sadness on a global scale in many of these stories (all the Martians die, most of Earth is ruined), he also zooms in to look at the sadness of individual characters. We have to say, Bradbury's presenting a pretty grim picture of humanity's future.
The pervading sadness of The Martian Chronicles suggests that humanity is doomed, no matter what schemes it develops to save itself.
The ultimate sadness in The Martian Chronicles is that time continues to move forward, changing everything we love.