Nothing more than one gigantic mini-game.
The two modes open from the beginning include a point system and a distance mode. Controlling the game is quite simple - use your stylus to draw clouds, draw circles around enemies, and blow in the mic to dispatch the clouds.
And that's it.
The difficult part comes from manipulating Yoshi while the level pushes you forward, much like the last level of Super Mario Bros. on Nintendo. Drawing circles fast enough or spitting eggs to finish your enemies involves quick hand and eye coordination.
I suppose the easiest way to sum up the experience is a warm up for your stylus happy hand. Practice makes perfect, but in this case it just means your ready to move onto more fast paced stylus games such as Ponit Blank DS. Cheers!