The first Donkey Kong Country had several levels, great music, very appealing graphics, creative bonus stages, amazing background effects, and very well-designed levels. To me this game was amazing.
In Donkey Country 2: Diddy's Kong Quest, everything got even better. The boss battles were a lot better than before, the music was better, and the stages were even better. Even the bonus games were better, after successfully completing each bonus level a kremkoin would be gained. The kremkoins could be used to access the Lost World Levels which were very challenging. Along with kremkoins there was also DK coins which can be found in each level and are pretty much just like the banana stash in the first Donkey Kong Country. This game is definitely worth completing with 102%.
Donkey Kong Country 3: Dixie Kong's Double Trouble added a new map style, where you could move your character around in an open environment to travel to different places in the world map. It was definitely new, although really not too necessary.
The bosses in this game were also quite creative. Like all games in the series, the stage design was great. Although the music wasn't as effect as Donkey Kong Countr 2's. It's a great game, and worth playing all the way through.
To me, Donkey Kong Country 2: Diddy's Kong Quest was just right, definitely the best in the series.