I know it's terribly last millennium but I do enjoy a book, but I ain't read them all so I thought it would be nice share I bit of knowledge on the old literature front.
I pose the question, what is your favourite SciFi novel and why?
I'll get the ball rolling with mine,
Starship Troopers by Robert A Heinlein. It's a genuine satire (not a parody like the joke of a film) with something to say on the susbject of personal and social responsibility versus rights and entitlements and a increasingly prophetic comment on modern society. It provides an interesting take on military efficiency and cooperation wrapped up with with Soldiers in armour fighting a truly Alien foe (rather than funny coloured humans). Despite common Internet "wisdom" I don't see it as the inspiration behind the Adeptus Astrates, who share very little with the mobile infantry other than that they wear armour.
Notable mentions go Frank Herbers Dune, which I believe is the real inspiration behind 40K and Joe Haldeman's forever war a very interesting take on how a war against an alien spieces would go and how it would affect the participants.