I didn't expect this game to be as fun as it is. I downloaded it because it was free for a limited time and I kind of expected to end up uninstalling but I was pleasantly surprised.
The gameplay is easy to figure out. Basically, zombies shamble towards your house and you have to try to stop them by using plants. You get different types of plants as you go through the levels. There are some that shoot peas, some that have effects like slowing zombies down, cherry bombs that explode, and so on. The amount you can plant is dictated by how many sun points you have to spend and you can plant sunflowers to give you more sun points.
Overall Plants vs. Zombies is fun to play and puts a good spin on tower defense gameplay. I think its worth checking out if you don't mind paying a bit for a decent game.
Hmm, I just noticed that at the time of this writing it doesn't appear to be available in the android marketplace. I got it through a special offer that isn't available anymore. Any readers with an iphone, ipad, or similar should be able to get it, but android users may have to wait or find an alternative place to purchase it from. There is an android version of it though since it works on my phone just fine. Look around and maybe you'll even find it for free.
Screenshots below(sorry for not rotating them, I'm lazy and posting from my phone):