Basically, that he was not my favorite of the old time science fiction writers (that honor went to Heinlein, obviously, but also Ray Bradbury, which is something I don’t think a lot of people have guessed), but on the other hand I remember quite vividly faking a sprained ankle in 8th grade gym class in order to keep reading 2010, which had just came out and which I felt was more important to me than climbing up a rope or whatever. I still do, come to think of it.
What I liked about Clarke, however, was that he was a science fiction author who walked the walk as well as talking the talk: He was a scientist, and a pretty good one, and he was also an optimist about what science could do for us (“The Nine Billion Names of God” notwithstanding). One does wonder if another science fiction author will also be such a world historical figure; you didn’t have to read science fiction to know who Arthur C. Clarke was, or that he was a writer and thinker who commanded respect.
One other thing. I can’t remember which book it was — I think it was 2061 — he had one character (I think it was Heywood Floyd) talking to another character, who was gay and celebrating an anniversary, and Floyd mentioned something about the gay character being in a relationship longer than most married couples he could think of. I do believe it was the first time I had ever thought about the idea of same-sex couples living as married couples, and I think I recall thinking that seemed perfectly reasonable to me. Leave it to science fiction, and to Arthur C. Clarke, to drop a then-radical social idea into my head and make it seem perfectly normal. And of course now same-sex couples can get married, in several countries including in the US (albeit in the latter case in only one state; even so). Glad Clarke got to live to see it.