I must admit having a rather strong love of Free Cell myself. I have a roughly 95% win rate, where with solitaire it's rather on the lower end, probably 15-20%. Partly that is the style I play (3 card draw, Vegas scoring) makes it much harder to win, but that isn't the goal. My goal with solitaire is simply to just break even damnit. They each have their purpose. Solitaire for 5 minutes of turning my brain off and seeing how it goes, Free Cell for trying to think my way through the challenge.
Free Cell is wonderful because it embraces a simple rule set, with clear objectives, and challenges you with rather devious implementation. The fact that your grandfather enjoys it shows how wonderful games can be for crossing cultural barriers.
P.S. I am toatally going to try and beat the impossible game now, 11982 here I come.
EDIT: Yeah, when they said impossible, I should have known.