Along with Fantasy, Science Fiction is one of my all-time favorite genres. Maybe it's the badass future technology, or the wide-arching storylines that can span millenia. Or maybe its the fact that the future, by its nature, cannot be known, so the creators of sci-fi works essentially have a no-rules sandbox in which to do their world-building.
It is difficult to describe why Science Fiction gives me such a sense of exhilaration and awe, but Tim at PopCrunch's description does a noble job of doing just that:
"Science Fiction writers—much like their cousins over in Fantasy—are renowned for being able write volume upon volume of prose, great tracts of novels, seemingly without end. Often these tomes are filled with nothing so much as overly lengthy location descriptions and predictable plots. However, some of the true greats of Science Fiction have surpassed the limits of the form, and created vast inter-twined plots set across multiple novels, and multiple time periods."
Admittedly, I have not read a few of the series on this list (to my shame, Asimov's Foundation Series is amongst them) but I will definitely sink my teeth into all of them, and many more, before I kick the bucket.
And, without further ado, here is Tim's list of the 19 Greatest Science Fiction Book Series.