Really I appreciate the scientific books that he wrote for the laymen. Reading them is how I was catched by science
I haven't read any of his sci-fi storiesn but seems that the series foundation has rather success
I never much cared for Assimov. I read his books, and they weren't terrible, but - in the face of such authors as H. G. Wells, Orson Scott Card, Nancy Kress, Anne McCaffrey, Robert Silverberg, Greg Bear, Aurthor C. Clarke, even Frank Herbert (and many, many, more) - Isaac Assimov is (IMO) rather weak.
Asimov is one of the best, but don't forget Bradbury in addition to the others mentioned above. For me Azimov, Bradbury and Heinlien are top of the pile. (Orson Scott Card has some good stuff but has not been around long enough to rate with the old timers!)