There isn't much to say about Donkey Kong Country Returns 3D, given that the original Wii game is a known quality. Retro Studios' 2D platformer was always a looker, playing with depth in a way that made the game feel far more dynamic and exciting than other games in the genre. It was a perfect fit for 3D, which is why it transitions so well onto 3DS. In fact, it's probably my favorite use of 3D on Nintendo's handheld so far.
Outside of Super Mario 3D Land, not many games have enticed me to turn the 3D slider on. And even when I turn it on, I usually keep it on the lowest possible setting. With Donkey Kong Country Returns, however, I found myself wanting to keep the 3D running at maximum strength.
Although the 3DS port (handled by Monster Games) loses quite a lot of detail compared to the Wii original, the 3D effects are absolutely superb. It's hard not to be impressed when Donkey and Diddy Kong are shot out of barrels, and pillars are falling towards the screen. This is definitely the technical showcase 3DS has been waiting for.

Those that played the Wii original probably have holes in their walls, thanks to its borderline-psychotic difficulty. The 3DS version offers an easier experience, with Donkey and Diddy Kong equipped with three hearts instead of two, and being able to use items to more readily recover from failure. I welcome the changes, as I found the original a bit too stressful for my tastes--but gamers that expect more of a challenge can play the game with the original Wii settings.
While DKCR's winning gameplay and amazing 3D visuals will appeal to 3DS owners that missed the game's original release, do Wii owners have reason to double-dip? Probably not. The 3DS version is easily the better version, and it also includes a special "World 9" not included in the original Wii release. However, this extra set of levels requires beating the game all over again. (There's no way to skip ahead to play the new content.) While eight new (challenging) levels might be reason enough for the Donkey Kong faithful, for most it won't be enough to warrant another purchase.
Donkey Kong Country Returns 3D will be available on 3DS on May 24.