I'm about a third of the way through Foundation by Isaac Asimov. Really quite liking it so far.
I'd say start with Foundation if you want a gigantic space epic spanning hundreds of thousands of years and light years but start with I, Robot if you want a series of short stories about his famous 3 laws of robotics. They sort of go in opposite directions, one out into space, the other into the logic or a purely logical being, both good, but very different feeling.
I just finished The Caves of Steel. I read it based on a high recommendation from a coworker that said this is the book to start on with Asimov. In the end, I thought it was a horrible book. It's been a long time since I've ready Hardy Boys, but I kept feeling that it was reminiscent of that series. I thought the story was bland. The environment wasn't interesting. The mystery wasn't complicated in any sense. I would have been OK with those things, if only the characters were interesting. If anything, I disliked the characters, but not enough so that it made me connect with them even on a negative level. The one redeeming value I gave the book was that it was short enough that I didn't feel like I lost a significant part of my life by reading it. I probably won't go on to read any more Asimov, but I am still curious because I see comments like "Greatest science fiction of all time" when Asimov comes up.
Asimov wrote a lot. Extremely prolific. A lot of it isn't worth your time, but Foundation is one of the high points. A lot of his work, like Heinlein's, seems dated since he wrote it so early in the technological revolution (that we're still in).
Cheers, its the best epic story that I know of. Touches upon some great philosophical sentiments and has bits and pieces of everything I wanted in a good series
Absolutely fantastic series. I won't ruin anything for you, but just know that it keeps getting better!