I read alot, primarily Science Fiction. The wife and I have many thousands of books, it's the side benefit of having worked for publishers in our lifetimes.
As I see he answered you with Spider Robinson...I was going to say that if he mentioned "Kim Stanley Robinson", he would immediately discredit himself. Red, Green, Blue Mars have to be, without question, the worst books I've ever read. Took me FOREVER to get through that dreck.
If you're looking for some good "old School" hard science fiction material and you've not read him before, check out Jack Chalker. One of my favorites. He recently passed so his works are complete.
Chalker's output is excellent. But I prefer it for dessert, after a heavy course of H. Beam Piper.
Jack Chalker, OK, great, I'll check him out too. Thanks very much.