19. I am a huge KSR fan and I just finished "2312" today.
I also love his Mars trilogy (2312 takes place in the same universe as the Mars trilogy), minus the few ideologically-based factual errors like his thinking the Minoans were matriarchal. His Global Warming trilogy was also excellent.
The Years of Rice and Salt is a real head trip, though as a history buff I had to suspend my disbelief in the unlikeliness of his alternate history.
Also, It was weird realizing that most of the "First 100" colonists in his Mars trilogy would be of my Millennial Generation.