The future history of our colonisation of mars.
The episodic nature of the story allows it to be told over many years and to cover events on earth and on Mars. Many SF writers struggle to flesh out the humanity in their characters because the ideas and situations are more important. Bradbury manages to create a miniature person in only a few pages before we move onto the next set piece and he manages to deal with issues like nostalgia, jealousy and colonisation in a very memorable way.
I sometimes find Bradbury to be a little soft. His ideas don't seem to have a hard logical edge and his work is very literary. I find him almost Ballardian in some passages (I'm thinking of Vermillion Sands and some of the SF work of Ballard here rather than the urban dystopia stuff). At times in this collection of episodes I was a litle bored and I felt that Bradbury was trying to seem worthy and forgetting to be entertaining. Bradbury is a huge figure in SF and I have read Fahrenheit 451 (review to come) but I don't know if I would want to read more. Maybe the short stories are a good place to go next? Suggestions welcome.
Overall the concepts in the Martian Chronicles are a little dated but this is not a problem as we can now view the work as a piece of retro 1950s SF written on the cusp of the space age when people still entertained the idea of a martian civilisation. The novel is wonderfully wistful and eerie in places.