Can't believe all the PvZ haters, it is such a fantastic game. It starts off simple but becomes much more complex later on. Try not to think of it as a tower defense game so much and just have fun for once! The art style, sounds, and overall humor really make the game an instant classic. The gameplay is very fun on the iPhone (even more so on the iPad) and it's the first game I recommend to everyone who buys an iDevice.
Sometimes a game doesn't have to be impossibly hard to be fun, there is enough challenge in Plants vs Zombies even for the hardcore tower defense players. Mainly because it is not at all like most tower defense games and has plenty of varied mechanics as the game progresses.
are you on their payroll? the game is terribly easy, you can set the same plants in a certain position that would get you past every level, no new updates, no survival, it's basically a waste of memory space when you beat it once