“Early days” is an ambiguous term, as is Science Fiction. But let us say Jules Verne represents “early days.” The Science fiction bonanza of the 1950s (Bradbury, A.E. Van Vogt, Isaac Asimov, etc.) features explorations into human psychology and whether there was such a thing as “human nature.” Would the future, with its new horizons, change or acknowledge or justify human nature? While there was some discussion of technological advances (as in Clockwork Orange) the real subject was aleways what was meant by human nature. Today, technology having accelerated, the Science Fiction question is what new understandings about our world will manifest themselves? A fundamentally different exploration – not only of space exploration (Star Wars, etc.) but of technological alterations of our reality (think of Inception) -- takes over the Science Fiction imagination. There are few new “utopias” to explore, but many “dimensions” – I see SF stories following the String Theory, wormholes, etc. – movements through layer of time.
Asimov is an amazing genius. His Foundation series was basically an alternative human history that explored human psychology, mob mentality, and the progression of civilization. His robot novels (he was the first to coin the word positron, and robotics) explore the limits of scientific technology and the necessity of human ingenuity for problem solving. The early 1930s sci-fi work was mostly short stories for magazines such as Amazing Stories. Asimov was one of the first few sci-fi authors to have successful novels.
More modern authors include: Douglas Adams, Neil Gaiman, and Orson Scott Card.