Zack and Wiki is basically a puzzle adventure. It's broken into levels where you try to get the treasure in each level. There's a puzzle you have to solve to get the treasure.
The puzzles are level-based movement and action puzzles like you'd find in Lost Vikings, Lemmings, etc but the controls are similar to the early-90's Kings Quest and Space Quest games. You use the Wiimote to point and click for movement and interacting with objects. It's a fun genre but if you struggle on a small part of a level you'll find yourself replaying the whole level over and over again and that can get very repetitive. Fortunately, the levels are short enough that you're not repeating a whole lot of actions and since it is level-based, doing something wrong early on isn't going to keep you from finishing the game later on. (Anyone who didn't pick up that stupid laptop in the first part of Space Quest IV knows what I'm talking about here.)
I think it's a decent game but there's no way I'd pay full price for it. The good thing is that you can probably beat over the course of a rental or two and replay for it stinks anyways. (Generally, the only thing that makes a level worth replaying is to see if you can find a more efficient solution.)