Wario World could have been an interesting title for the platforming genre, but it just comes up short.
Wario World goes off of the premise that Wario's treasure has turned into creatures, and he has to defeat them to get his moneyz back. So, yeah, this isn't exactly a gripping narrative, but you shouldn't be going into a Wario game expecting that.
The controls in Wario World don't exactly improve on anything thats already been done, but overall its ordinary and not exactly a bad setup.
And now, it's time to sift through the faults or Wario World. First off, and probably the most important, this game is far too easy and far too quick. You can go through and find every hidden artifact, which does improve on the time and difficulty just barely, but to make it through the main game is incredibly straight forward. Another fault is the fact that every enemy type in the game is very uninteresting, as they are just fitted with different skins that accompany each stage. The enemies don't even change their attack patterns anywhere throughout the entire course of the game. Its simply lazy.
Back to the pros, Wario World presents "Treasure Rooms" in each stage, where you have to solve a puzzle in order to get a set number of red diamonds which are needed to end the stage. Even though you only need about three diamonds per stage (out of the ten or so the game allows you to carry), these treasure rooms are undeniably fun, and a few are actually very frustrating toward the end of the game (which is a relief seeing as the rest of the game is so easy).
At the end of each stage, there is a boss battle that accompanies the themes of each stage. These bosses look quite creative, however they ended up being very easy to defeat. Also, if you die in any point in the game, all you have to do is pay a small amount of mula and you are re-spawned right where you die. It's just too easy.
If you end up falling off the cliffs of a stage, you just have to endure a small minigame and lose an extremely small amount of coins in order to continue your game.
So, in the end, the stage design and boss character design end up looking quite creative and varied, but that does not hide the fact that that the game is undeniably easy and somewhat lazy in the sense of the basic enemy design.