It must be impossible to play Kirby's Epic Yarn and not find yourself grinning merrily away like a demented clown. It's far and away the cheeriest game of this generation.
The story is beautifully presented in the style of a children's book, beginning when the evil Yin-Yarn sucks Kirby into a magical sock after the pink blob ate his tomato.
So Kirby finds himself in a material world called Patch Land - the ground is made out of denim, the backgrounds are cloth, while creatures have buttons for eyes. What's more, Kirby himself is now made out of thread, meaning that he no longer has the ability to suck in and eat enemies.
Yin-Yarn has split this Patch Land into seven different pieces. The only way to patch it up again is to find the magical pieces of thread that are being held by the world's biggest baddies, and use them to sew all the different regions back together. It's nonsensical, but adorable.
Epic Yarn is played with the Remote on its side. You press the 1 button to make Kirby grab onto things using a loose piece of thread. You can grab hold of your enemies and turn them into balls of wool, which you can then throw at other enemies.
It's the ability to interact with the scenery that makes Kirby's Epic Yarn a joy to play. Rarely does a platform game make this much use of the background environment, and in such a creative way too. You can yank over part of the background so that it creases over and makes a gap narrower, or peel back a sticker that's disguised as an object to reveal the treasure hidden underneath.
In the other two games, it could sometimes be a little tricky to interact and work together, whereas in Epic Yarn it's a piece of cake. For example, simply pressing the 1 button from a reasonable distance to grab your partner is significantly less fiddly than standing right next to them, holding the 1 button and shaking the Remote (as you had to do in New Super Mario Bros. Wii).
Since it's so easy to do this, beginner players can now help too - by grabbing their partner and chucking them into enemies (which defeats them) or tossing them to hard-to-reach locations.
Co-op is also the best way to experience some of the awesome transformations Kirby and Prince Fluff are capable of - such as turning into a huge robot with a rocket-powered boxing glove or a dolphin on a surfboard. When two people are playing together, the controls are split between them, meaning that you'll need to work together to get through. For example, the aforementioned robot lets one player control its rocket-powered arm by pressing a button and tilting the Remote. Meanwhile, the other player is in charge of the robot's movement and its other arm, which can be used to punch nearby enemies.
Each of these transformations completely changes the gameplay mechanics, to the point where each level is made to feel like a completely different game. You could transform into a mole on one level and find yourself digging your way through underground tunnels made of cotton wool, while the next could see you turning into a UFO, flying around and sucking enemies into your tractor beams, before using their power to blast out electric shocks.