Notable authors are BookShelved:OrsonScottCard, BookShelved:HarlanEllison, BookShelved:ArthurClarke, BookShelved:IsaacAsimov, BookShelved:RobertHeinlein, BookShelved:DouglasAdams, BookShelved:StanislawLem and BookShelved:RayBradbury. Actually, due to the effect of the third description above, some authors, including Harlan Ellison, prefer to consider their work SpeculativeFiction and label the mainstream of this genre SciFi, pronounced "skiffy". Subgenres include "hard" and "soft" science fiction, space opera, and CyberPunk.
"Space opera" focuses is on huge, overarching plots.
CharlesMatthews: Depends a bit whom you read. I'm heavy into BookShelved:CJCherryh, who riffs on alien mentalities, BookShelved:JackVance for the style as pure entertainment. Those writers are doing some sort of AnthropologicalThoughtExperiments?, it has been argued. The 'scientific progress' thought translates as technological advance, with its consequences for ... society first (nineteenth century ideas about industrial revolutions and frontier lives prominent, in a sort of implicit dialogue with Marx), human culture and mental patterns a long way after.
JosefDaviesCoates: One of my all-time favourite books is Last and First Men by Olaf Stapledon. Incidentally it was also the book that most inspired Arthur C Clarke - I haven't read any of his books, but we've all seen the Stanley Kubrick film 2001: a space odyssey