Asimov's fiction is simply amazing. Partly because he never simply wrote novels that had futuristic overtones. His stories always turned on logical, philosophical, or sociological principles and ideas. For example, his fine Elijah Bailey series dealt with a very realistic and gripping society. Of course, they're also excellent murder mysteries, and they're engrossing tales, but his construction of a future society is so realistic it's astonishing.

In response to the issue of his "not being able to write about aliens," this really is kind of a misdirected critique. As he said in a foreword somewhere or other, he actually did write some early stories that contained aliens. His stories often portrayed the aliens as being superior to humans and this was intensely disliked by the editors of the magazines he wrote for. They always made him alter his stories, which displeased him greatly. So, he stopped writing about aliens altogether. Instead, he turned his attention to robots and humanity and never looked back.

I also would like to recommend that everyone out there in E2-land read the Robot City series--they're fantastic! The idea behind them is that Asimov came up with a basic idea for the series and then let other writers take it where they wanted. Each book is by a different author who took up where the last one left off, with some moderate guidance and ideas from Asimov. It's good stuff!