Same friend who introduced me to Harry Turtledove's Wroldwar series talk to me a lot about Isaac Asimov's Foundation series. Also I've heard a lot about Asimov's "three laws of robotics and generally how he brought robots to everyone's mind. So I started reading and got through books, all of them. I've started with this: http://scifi.stackexchange.com/questions/2335/what-order-should-asimovs-foundation-series-be-read-in, basically all of the robot stories then all of Foundation stories and finally the rest of 101th "mystery" short stories and novels. Nice thing about Asimov's novels is they are almost all "mysteries". If you are like me born 50 years after most Asimov's work was published and don't have "mystery" in your genre list, it's broader term for crime/detective story (or "krimić" in Croatian). Broader in the sense that it doesn't have to involve murder or any crime but still develops as a regular detective story, something not fully described happens and protagonist spends 500 pages collecting clues to reveal the big picture. That mystery part is the reason why his novels are so addictive.
Robot stories
Back to robots and the famous three law of robotics. First thing first, Asimov's robots are not what we call a robot today, at best they are androids (not Android but lower case android, as robot with human form) and they have very human-like way of thinking. Second thing first there was no Internet nor proper transistor powered computers back then and it shows in his work. When you see a word Multivac (also described as large as room or whole building) you'll know how little he thought about the future of computers. Back to robots and the famous three law of robotics. In Asimov's novels "robots" are metal humans with three mental restrictions. Aside from those restrictions they have normal human hopes, desire to get free from oppression, have fight or flight instinct and whole slew of human characteristic that you'll not find in modern military drones, mining equipment and mine sweeper robots. Also Asimov didn't invent any true laws of robotics, just wrote a stories that introduced reader to metal humanoid beings (MHB further on) with three particular mental restrictions and then played with what ifs. What is this restriction was taken literally, what is there was MHB without that restriction, what if there was MHB with this or that ability and so on.
In the end, despite having all technology depicted wrong (oh I have to rant about it even if it happens in the middle of the sentence like this, in one story the author postulates that is more feasible to control machinery on Mercury with special brain on Earth then to land a computer on Mercury and then believe the reader won't ask whether 25 minute lag would be a problem), robot stories were fun to read. Those where MHBs are not object of "what if" are even better and those that are prequels to prequel to the Foundation series are golden.
Foundation series
Which brings as to "great man theory". The Foundation series is more about people that defined fictive future history of mankind then about how famous psychohistorians' plan for the whole galaxy developed. Similar to robot stories there is a path the humanity is supposed to follow and author throws various what ifs that derails it but this time protagonists and objects of "what if" are humans. And each such human is an epic thinker that accomplishes great deeds through careful observation and planned action. End of the series is a bit weak, Asimov kind of went hippie there but as I've learned recently, he planned to write more, didn't have right inspiration and died. Other authors continued his work. I'm a bit skeptical but I might give them a try.
What Asimov had inspiration for was more great man stories so he wrote prequels to the Foundation detailing the life of the first psychohistorian. Who was in love (platonic, no sex, please no Hollywood crap here) with a robot, ups, MHB (at some point in robot stories MHBs became so sophisticated that some are hardly distinguishable regular humans), "mathed" his way out of deadly dangers, ruled the galaxy for a while, laid the way for new galactic empire and helped certain MHB with "zeroth law of robotics".
Robot series
Which brings as back to robot series. There were great men too, Susan Calvin (didn't say all are male), Elijah Baley and I'd include even MHB R. Daneel Olivaw. I've found stories centered around Elijah Baley most fascinating. In the first there was a murder which means mystery, in the second there was a clash of vastly different cultures, then a story about a third vastly different culture and finally a story about evolution of galactic proportions going from subtle to global. And there are toilets, vivid, detailed description of a toilet in each culture. On the serious side worth mentioning are differences in how families function, on the one side are our normal mother-father-children groups while on the opposite end is absolute separation of children and parents.
Other stories
Other stories cover so many subjects, from classic "somebody died, who is the killer?" detective story to an old lady trying to remember a street name. Some stories are weird with assumption that humans would resent going
outdoor which was probably work of author's claustrophilia. And there are puns. I'm not American, English is not my mother tongue so I don't find them funny (pun gets lost in translation) and some I didn't get before looking up because they referenced some song that was popular in bygone century on the other side of the planet. But most of the stories are good read. It also helps that Asimov studied biochemistry. Golden egg goose is golden.
