I beat Donkey Kong Country 2 with my girlfriend this morning, then picked up the 3rd one and played through the majority of it.
I couldn't get over how cheap DKC2 was. I get that the levels are tough, but most of the later levels come down to memorizing everthing, since the sprites are so big that things come at you from offscreen all the time. That, and you actually have to spend coins to save your game.
That said, the 3rd game addresses a lot of these issues, and I'm really enjoying it.