This is actually Retro's secret project that they have been working on. It's possible that they may have another game they are working on. But there isn't much evidence to prove this.
Anyway, here's a vid:
So I think the biggest feature for this is the 4 playable characters. There is Donkey and Diddy of course. But Dixie is also revealed and supposedly one more character. My guess is Funky Kong. But it's possible to be Cranky to.
There is also more 3D camera movement to open new areas and gameplay elements up.