Tropical Freeze for me.
I'm a huge fan of the original trilogy but I found that Donkey Kong Country Returns, while having amazing platforming sections, just felt a little soulless. Tropical Freeze seemed to address this issue ( at least for me ) with it's more varied and colorful levels.
One thing that this game had going for it over Returns was David Wise. The inclusion of Wise raised what was already an amazing game to God tier levels. For me, it showed just how a fantastic soundtrack can take a great game and elevate it even further.
This track ( Seashore War ) is one of my favourite pieces of music from any videogame I have ever played.
https://www.youtube.com/watch?v=Boqy0Q-4c_M
Special mention goes to Captain Toad. This is a game I also adore.
I've always loved Toad as a character ever since playing Super Mario Bros. 2 as a kid and to see him in his own game was a delight. It has that typical Nintendo gameplay style to it, where the game is easy and short if you just go from point A to B, but once you start trying to get all the gems and getting times under par, the Nintendo challenge really comes into play.