"At this very early point in its history, it's the best-selling game PopCap's ever had," said Popcap's Garth Chouteau to Gamasutra. Plants vs. Zombies combines the simple, addictive nature of PopCap titles with the strategy of tower defense and the reliable attraction of zombies, making for a broadly appealing title.

"At this juncture, we don't worry much about 'casual vs. hardcore'--we try to make games that will appeal to both audiences more or less equally," said Chouteau. "In this short attention span century of ours, this can be tricky since people tend to judge things quickly."

Added Chouteau: "Thankfully, Plants vs. Zombies is engaging enough that people end up spending a ton of time in the game before they really realize that an afternoon has just evaporated."