Wario Land: Shake It! isn't exacaly the most chalanging game you'll play, but it will be one of the most fun.
The story, as in any wario game, isn't exactly confusing: A bad guy has stolen some treasure (And a princess) And you have to save it (and her) and win the day. It's Simple stuff and not really needed anyway, but it's still a good gesture.
The gameplay is about as simple as the story: Run around, get money, save the guy at the end and run like hell back to the beginning. It plays quite a lot like The unofficial sequel to WarioLand 4. It does, however, throw around some new things in the later stages, like spinning polls, sub-War-ines, and uni-buckets, and includes some missions and hidden treasure for the complete-ists. The missions range from "get enough coins" and "get to the end before the timer hits ___," To somewhat annoying ones like "Don't get hit" and "Don't kill any enemies," And the treasures are well placed through the level. If you just run through the stages, you'll have the game done in around 6 hours, But the missions, secret maps, and treasures add around 10-30 hours to that, depending on how good you are.
And you'll want to do the missions, because it unlocks the background music. And why is that a good thing? because the music is so brilliant. In fact, the entire game has obviously been built around making it look and sound as good, cute and awesome as possible. The music can change from relaxing to energising in an instant, and it always fits the theme of the stage. The stages look fantastic, the enemies look almost too good to actualy kill sometimes, The animation moves as smoothly as a greased covered ice cube on a icy hill, Wario can actually be pretty funny at times and the beginning and ending scenes of the story look like they're actually from an anime. I'm not kidding. The entire look and sound of things will make sure you never get annoyed on a particularly difficult mission. Case in point: One mission saw me running through the same part around 30 times, only to find out I didn't complete it anyway. Of course, I was mad. I went on to the next level fuming, started to calm down with the music, then saw wario's "landing from a spin" animation, where he pulls a dramatic pose, and his fat belly bounces up, with matching sound effects. Something about it just made me want to laugh, and suddenly I didn't want to smash my controller anymore. This is about the first time I've ever seen a game unintentionally piss me off and then calm me down immediately afterwards.
in conclusion, Wario land: Shake it! Is sort of like the "Yoshi's story" of the wii: It's not challenging, and it doesn't brake any boundaries, but somehow it still manages to be amazing to play and just as good to look at.