[Oddy]

What are the best books where entire world's aren't created and complicated space systems, etc etc aren't explained to an extreme level.

Something like Ender's Game where the world is there, yet it isn't so in depth as a book like Hyperion (which was still excellent).

[Fitzy]

How about Forever War & Gateway, both set in a future Eath that doesn't require alot of explanation about the world.

[ArthurFrayn]

Altered Carbon
Vurt
Old man's War

[cougs]

Childhood's End
1984
The Foundation Series - While it does take place over quite a large area, there is little to no exposition on well...pretty much everything.

[phil_geo]

Altered Carbon is maybe one of the most complicated worlds I can think of. Between the entire sleeve thing that you have to get your head around, the vast changes that have happened to the world (both societal and geographical) and the hundreds of years that pass during/between stories and books, it is a book that requires a lot of understanding of complicated systems.

Maybe I'm misunderstanding what the OP was asking for, but Altered Carbon may be a little too much complexity in the world-building department for his criterion.

[ArthurFrayn]

Altered Carbon was not as complicated, for me as something like Hyperion. As far as the sleeve society-unless he outlines that better in other novels, I found I had to take that whole concept with a grain of salt in terms of how it would work and why anyone would want a setup like that.To me it's merely a backdrop for good a CyberNoir drama.
And I didn't really find it as heavy going with regard to concepts as Gibson, Stross, or Swanwick when they do stuff like this. To me Altered Carbon was a plot driven novel, not an ideas novel.

[Fung Koo]

Most Heinlein fits the criteria. Just steer clear of multi-volume space opera epics and you'll usually do alright.

[ArthurFrayn]

Maybe Use of Weapons as well, it's a nonlinear novel, but the background universe is not overly intricate. Again, at least in that novel.