The Snowmads have been very well-received, with some saying they're better than the Kremlings.
The music is amazing.
The final boss fight against Lord Fredrik.
Just about every boss fight counts, especially on Hard Mode as solo Cranky, and the aforementioned music certainly helps.
Fan-favorite Dixie Kong makes her triumphant return and is even better than ever. She can even get a little lift from her ponytail while riding Rambi.
Cranky Kong, after years of sitting back and letting the others do the hard work, finally joins in on the action, albeit possibly against his will, given that he doesn't have much choice.
One thing that has to be mentioned is Cranky's pose before a boss fight- He slams his walking stick into the ground, bouncing it up in the air and strikes a pose before catching it, all while glaring at the boss. It sounds silly (and kind of is), but it looks badass.
Defeating Squiddicus in "Irate 8" after he plagued Donkey Kong in both "Stormy Shore," in Returns and the aforementioned level.
The new leaderboard system for time Trials that lets you view replays of other players' runs. Needless to say, the world record run of any level is a sight to behold.