I loved it as a teenager, i'm re-reading the whole series, starting from the robots, and i'm really not enjoying it as much. The characters are pretty bi-dimensional and the few female characters are really badly written, sometimes even downright creepily (he later blamed it on having written it as a 20something virgin), the writing is a bit dull and the plots too often rely on deus ex machina or some plot armor. Probably some today wouldn't be published (one revolvs around a mistery of a "lemonade death" that's pretty ridiculous), but for when they were written they were absolutely revolutionary, some of the concepts introduced really amazing and they have influenced most of the scifi that followed.