I'd been wondering why the game Plants vs Zombies had been so popular for years now (since supplanted by Angry Birds, which I honestly don't think is that great a game.) Starting on the PC and then ported to virtually every other game system, I recently got the game for the DS, and now I realize why this Popcap-created game is still popular...it's very. very fun.
An organic version of the tower defense formula, you use dozens of imaginatively created plants to defend your house against waves of many different types of zombies who want to snack on your brains. By gathering sunlight beamed from the sun or generated by sunflowers, you can plant peashooters and walnuts to fire upon or block the zombies advance on your house. However, you can only have a certain number of plants on which to call upon in each level, although you can buy more spaces to hold plants (or 'seed packets') as the game progresses.
As I said before, this game is a hell of a lot of fun, not to mention very funny. There is an in-game encyclopedia that describes all of the plants and zombies in the game, and it is well written and hilarious. The game can be nerve wracking, as you frantically gather sunlight and plant plants to stop the zombie hordes. Although it seems limited, with the playfield only being around your house, there are different scenarios that keep gameplay fresh, such as zombies attacking at night (in which you use deadly fungi and mushrooms, since they don't require sunlight, although they need to 'recharge' before another one can be planted). Or the zombies try to attack from the backyard, where you have a pool and need to put down a lily pad before you can set another plant on it.
The game uses the stylus for everything,and this works very well, in my opinion. There are also minigames that can be unlocked as you progress, and even a mode where you can create your own custom made zombie, or 'zombatar'. If you still have not played this game yet, I highly recommend this version. Now if you excuse me, I hear some zombies coming, and I've got some planting to do.