There are two major subgenres in puzzle games: things falling down (Puyo Puyo! or the seminal Tetris) and things switching places. While such simplicity should be boring (and in most other videogame genres, probably would be), in a puzzle game it's almost beautiful in a Shakespearean sonnet sort of way. With only a few basic rules, a good puzzler is both comfortable and pushy. We know how it works, yet in its familiarity it asks us to do better. Can we get a combo of three instead of just two? Can we move faster? Can we get 100,000 points and a free continue? If puzzle games are measured by their ability to make us ask more of ourselves, then Zooo for the Game Boy Advance does its job pretty well.
Zooo is a "things switching places" sort of puzzler. Players must capture animals by lining up at least three of the same kind of creature—three lions, three elephants, etc. Lines can be either vertical or horizontal; they're formed by flipping two animals that are right next to each other. Anybody who's played Bejeweled knows this drill, but the game is no less fun for that.
Of course, players who only concentrate on getting three animals in a row will get nowhere fast. Combos can be chained together as right angles (i.e. five animals arranged in both a vertical and horizontal row), or by simply letting the lines of falling animals work their magic. Sometimes a flashing "Special Panel" falls on the screen; clicking it makes all the animals of one type disappear from the board. Also, in every level there is a designated "lucky animal" that's worth double points and does a cute dance on the left side of the screen whenever it gets caught. If the player gets stuck, there's a stock of "binoculars" to help spot possible moves.
Aside from the main game, where players must capture a certain number of animals before time runs out to move on to the next level, here are several game modes in Zooo. They include Score Attack (play in a six-minute time limit), Score Attack (get 200,000 points), Tokoton (where the player moves to the next level by capturing 100 of one kind of animal), and Quest (where each level has its own mission, whether to "Get 70 animals!" or "Get the Special Panel to the bottom!"
I like Zooo. It's got few rules, cute characters and a soundtrack that isn't half bad. But liking a puzzle game isn't enough for me to spend money on it. With so many puzzlers available online, why should I pay $20 for something I can get for free? To turn a profit in this day and age, a puzzle game needs to be divine—and Zooo, unfortunately, is just a diversion.