Yeah Kim, Rachmaninoff was ahead of his time all right. I remember playing some of his pieces in school as well.

As for technical difficulty? Who knows, I don't suppose he is any better/worse than any other composer, that's always such a matter of taste. You know it done well when you hear it. There is a huge difference between dexterity and virtuosity; anyone can learn to pick the notes from a piece of paper, but very few can play them like they were meant to be heard.