Can you believe Record of Lodoss War was based on a bunch of D&D sessions? Personally, I couldn't really get into D&D, despite my geeky nature. Too many stats, dice, etc. I do like it as a storytelling engine, but the downsides outweigh the advantages to me. Meanwhile, RoLW seems like a heavily edited series of sessions, because there's no way things went this smoothly.
I did, actually, play some GURPS RPGs, at some point. I couldn't navigate that if you asked me now, I'd have to refamiliarize myself with it, but it was pretty fun. I even ran a superhero game once, though it was a hot mess. I kind of miss those days.