He was by far the best of the hard-core sci-fi writers. Other authors wrote long novels, but he wrote really sophisticated novels. They were the extrapolation of real life potentials, not necessarily fantasies, and that made them really vivid.

Poul Anderson recently passed away as well. And so did Claude Shannon, author of modern communication theory (real science at Bell Labs). Other famous writers are getting on in years too:

Arthur C. Clarke is about 85 years old.
Ray Bradbury is 82.
Brian Aldiss is 78.
Robert Silverberg is 68.
Gregory Benford is 62.
Nancy Kress is 55.
David Brin is 53.
Robert Sawyer is 53 years old.
Greg Bear is 52.
Orson Scott Card is also 52.
Greg Egan is 52.
Darrell Schweitzer is 50.
Paul J. McAuley is 48.
Stephen Baxter is 46.
Dave Wolverton is 46.
Charles Stross is 39.
Ted Chiang is 36.

Well they are all older than me. Ted Chiang is the youngest to ever win a Nebula Award. If you read his "Seventy-Two Letters" you will have some idea why.