Or a maybe a better example, Dune. Basically there is little link to the origins of humanity, so it's hard to call it a "speculative future". They also have space travel and advanced technology, but they don't really delve into the science of it. I mean if I recall correctly Dune has this weird setup where everyone has personal shield generators which render ballistic/laser/etc weapons ineffective so they all fight with... knives?
Is Dune not sci-fi?
What's interesting about the Dune series is the impact of ecology and environment on human evolution.
The Fremen and the Sardaukar are considered the pinnacle of warfare (given the convenient caveat imposed by the limitations of technology and weaponry) due to the harsh environmental conditions of their upbringing and the associated zealous religious fanaticism.
Frank Herbert later explores what happens to the Fremen as they achieve supremacy over the universe - they terraform Arrakis in accordance with their (planted) religious prophecies. Without the unifying struggle for water, they end up a pale imitation of a once great people and are referred to by Leto II as "Museum Fremen" who ape the traditions of their ancestors with no real concept of their significance. The film ends with them achieving victory - but it's a hollow one in the book series that is essentially diluted over thousands of years under Paul (briefly) and then his son Leto II.
When Dune was written, the ecological movement was in its infancy, with the seminal work Silent Spring by Rachel Carson having only been published three years prior. Considering the 10+ years that Herbert took in preparing to write Dune, he was at the forefront of asking questions about ecology and its effects on societal and human development.
Ultimately Herbert asks a number of interesting questions around the potential of human thought in the absence of thinking technology, the impact of prescience on governance and religion, the ramifications of galactic reliance upon a single commodity and the associations between environment, ecology, society and language.
He employs massive time scales to look at long-term impacts of short-term decisions.
From an origin point of view, the Atreides are literal descendants of Agamemnon, as Alia discovers when probing her memories.
In
Children of Dune, by
Frank Herbert, right before
Alia began one of her internal conversations with the
ego-memory of
Baron Vladimir Harkonnen an ego-memory called "Agamemnon" begged for some attention.
Therefore, Agamemnon seems to exist in the universe created by
Frank Herbert, but he could yet be a different character. It is very likely that the ego-memory Agamemnon is meant to be that of the historical
King Agamemnon of the House of
Atreus.
Brian Herbert bastardized this interpretation by inventing a new character called Agamemnon. My God he did a lot of damage to the Dune property.
When you say "they don't really go into the science of it", it's because Dune really isn't "hard" science fiction that relies upon the existing laws of physics as we know them. He avoids getting caught up in the limitations offered by a contemporary scientific perspective.
Meanwhile, an author like Alistair Reynolds (who is also an astrophysicist) probes a galactic civilization where one cannot exceed the speed of light, and thus those who ply their trade by moving across the stars accrue massive time debts in stasis. He explores the culture of these "Ultras" relative to the other societal factions that exist in his Revelation Space universe.
One really funny lesson is in the book Neuromancer, which is fantastic BTW, by William Gibson. He makes the mistake of using units in his novel, which ends up looking comically anachronistic within a very short period of time.
The person who stole the RAM chips from his computer is later killed for the same
3MB of RAM.
Whoops! I think most science-fiction authors now know better than to use existing units if they are talking about the future.
. Another one that just crossed my path is Kurt Vonnegut's The Sirens of Titan. 
