ARS: Plants vs. Zombies is filled with content and surprises, it's inexpensive, it runs on PC and Mac, and it's a version of the Tower Defense idea that actually feels fresh. The only downside is that for some the difficulty may take a while to ramp up, but it does get challenging as you progress and are faced with more, and tougher, decisions. This is a hard game to walk away from, and we're guessing the PC and Mac releases are only the beginning. This is a game that would work well on the iPhone, the DS, the PlayStation Network, and Xbox Live arcade; we can expect the addiction, just like the zombie apocalypse, to spread faster than we're comfortable with.
If you value your free time, find something else to buy. Just saying.