Funny enough, I received DKC and Earthworm Jim at the same time, and while my family was fascinated with EWJ, they were totally blasé about DKC.
I love the platforming in DKC (and especially DKC 2), but the rolling attack has always been a bit faulty, I think. You have to be on your toes and carefully gauge your momentum or you'll either stop short or spin right into another enemy, which makes it much less handy as a basic attack than just stomping or throwing a barrel.
As to why the games are so good, I guess it's just the combination of varied levels, fantastic music and pitch-perfect difficulty.