Critical hit! Direct hit!

[Edax]

I don't think I've played a game where stats didn't end up boring in the long run. Even WoW's Mastery (effect changed based on class specialization) fell flat.

Anyone played a game where stats felt fun and interesting? If so, what made them that way?

KOTOR had interesting stats. This came down to the fact that your character had a base of 10 and any point increase had a dramatic effect. In single player RPGs, you can get away with overpowered stat builds and abilities but with MMOs it's discouraged to have wildly varying balance. The problem with the multiplayer experience is that you can't make yourself special without making someone else angry.