The problem with Plants vs. Zombies - and it's arguable whether this is even a problem - is that it's going to be a long time before you appreciate how much value you've gotten for your ten bucks*. This isn't just a tower defense game in which pea-spitting plants hold off waves of zombies. That's merely a gateway to the rest of the game. A long narrow gateway. Once you've played through five worlds of tower defense levels, you'll find a whole lot more than you bargained for.

After the jump, I'll tell you what you'll find.

* Assuming you bought it on Steam and not directly from PopCap.

Plants vs. Zombies is surprisingly vast and generous for what looks at first like another one of PopCap's casual games. After running you through the paces, the folks at PopCap take the basics you've learned and put them through nearly every iteration, variation, twist, and unexpected contortion you can imagine, and then twice again as many as you can't imagine. Half the fun is discovering what games they've come up with. The other half is playing them. You'll get a taste over the course of the adventure mode, but it's just getting warmed up.

The long slow tower defense game is designed to introduce you to about fifty moving parts that will be jumbled all together by the time it's over. These fifty moving parts are the different plants you use to defend your yard, as well as the different kinds of zombies laying siege to your yard. It would be awfully daunting if it didn't take so long to unfurl. There are also distinct types of maps, based partly on sun power falling from the sky. You gather the glowing drops to buy plants (and also to keep you busy clicking while the game happens). But there's no sun power at night. Duh. That's when the mushrooms come out to play. And it's one thing to defend your front lawn. It's another thing to defend the swimming pool in the backyard. Which brings in the fog when night falls, so there's that, too. The gameplay comes on little cat feet, creeping up gradually so that even casual gamers can play. It's all about introducing a very basic rule set - zombies enter screen right and march left - and then breaking it and adding new rules and breaking those.

The basic tower defense is nothing particularly new, although it's as superpolished and charming as you'd expect from a PopCap game. On one side of the screen, the plant defenses have a great sense of thematic unity. On the other side of the screen, this is as cute an incidence of the dead walking the earth as you'll ever see. Here zombies get a little affection. They're slow, dumb, and gross, but they're loveable and funny, doing Sudoku, driving zambonis, and wearing inflatable duck life preservers into the pool. Everything is steeped in that PopCap we're-just-a-bunch-of-guys-in-a-garage/soccer mom-friendly love, from the bright and easy-to-read visuals, to the music that you'll probably never consider turning off, to the option to play in a window while browsing Facebook in the background. PopCap knows their audience. If anyone can bring the zombie apocalypse or a tower defense game to the casual masses, it's PopCap.

But for us serious strategy games, once we're past that adventure mode hump (it's maybe a matter of five hours), we've got plenty waiting for us as well. The mandate in Plants vs. Zombies seems to be offering a lot of variety in a really polished tower defense game, and letting players play it however they want. After the mandatory casual gaming in the adventure mode, Plants vs. Zombies is whatever you want it to be. A casual time waster? A survival mode doomed to eventual defeat? The challenge of making do with shuffled defense? Two-minute minigames? A slot machine? A Bejeweled clone? A virtual garden? A strategy serious-ish game? In reconciling the divide between casual gamers and strategy wonks, PopCap knows how to let a thousand necrotic flowers bloom.