DKC was pretty cool in its time. I didn't enjoy it enough to play it all the way through, but still a pretty decent game IMO -- and I was interested enough to try it again some 15 years later, and still managed get some fun out of it (but still didn't finish it second time around).
Sonic is very stylish indeed, but I think the speed factor ended up being a bit gimmicky for me in the end. The "run-around-quick-and-just-get-to-the-end" gameplay can get stale after awhile. One of the main reasons for a platformer is to well, jump around platforms and explore the settings, power-ups, etc, but with things moving around so quick, the "explore" part is a bit lost on Sonic games. Because of it, I never bothered too much with Sonic games after part 2.