My son (aged 7, and completely bonkers about Rabbids) has both the DS and the Wii versions of this game. He originally got the DS game, and played with it quite happily. Each stage is a little puzzle - how to get your rabbids from one side of the screen to the other, avoiding various pitfalls / traps that are in their way. As in most games, these puzzles become more complex the further you progress with the game.
We then bought the Wii version, and i don't think he's bothered looking at the DS game since ! The Wii version is far superior & much more enjoyable than the DS game. Rather than it just being a basic platform puzzle game, the Wii version is 3D, and you get to explore many different locations - collecting things, breaking things, and solving puzzles along the way. You also have the ability to customize your Rabbids, which can make for some very amusing looking characters ! (my son has made everything from a Harry Potter rabbid to a Frankenstein rabbid !)
Basically, if you only have a DS, then it's worth getting if you're a big fan of Rabbids. If you have both a DS and a Wii, i would recommend getting this game for the Wii. (if you want a good Rabbids game for the DS, try 'Rayman raving Rabbids')