Retro's new game is pure Donkey Kong Country with a bit of Jungle Beat mixed in.
Visually, Retro Studios' latest game, Donkey Kong Country Returns, looks like Donkey Kong: Jungle Beat. However, the side-scrolling gameplay is not far removed from Donkey Kong Country.

It is controlled with the Wii Remote and Nunchuk, and Donkey Kong (or Diddy Kong if you play two-player) can attack by ground-pounding, executed by a shake of the controller, or jumping on enemies.
I played a mine-cart level that was relatively tricky. At the outset, you went between two planes (think Paper Mario: The Thousand Year Door) and solved a puzzle that involved ground-pounding plants to find a hidden barrel. After finding the barrel in the background, you got shot off to a place in the foreground where you had to ground-pound a dynamite switch to blow up a wall in the background. After platforming your way through there, you arrived at the mine cart section, which was devilishly hard.

The game features two-player where each player can control a Kong on their own, or Diddy Kong can jump on Donkey Kong's back and shoot off his peanut gun. This was described as a "father/son mode," and is very much like the Co-Star mode in Super Mario Galaxy. When one player dies in two-player, they can come back if you have enough balloons (lives), but it places you at the exact point where the other player was when you came back. So, in the case of the mine cart level, you were screwed if the cart was moving. Unfortunately, this happened to me near the end of the mine-cart level.
The platforming also felt very slippery, but I guess that's all in the spirit of Donkey Kong Country. Fans of that series should be ecstatic for its return this fall.