As far as casual developers go, PopCap is one that stands out in people’s minds. Having poked their nose into social gaming more than once with games such as Bejeweled Blitz, and adding Facebook Connect to old titles such as Zuma, the port of another popular PopCap web game, Plants vs. Zombies, to the iPhone gave us some high expectations.

For those unfamiliar with the web version, the title is best described as the personification of “depth over breadth.” Ambiguities aside, it is a tower defense-style game in which zombies are marching toward your house and its up to you to defend it with some rather feisty flora.

Zombies approach on a grid, five spaces tall, and gradually work their way to your front door. The idea is to place – via tapping – different types of plants in their way to fend them off. Frankly, this is quite possibly the most amusing concept we’ve seen in a while, and truly shows what a designer can do with a little style.

Each plant is sort of a pun on existing plants and include defenses such as a basic peashooter, to a cherry “bomb,” to a potato “mine.” Of course, not all the style comes in the form of plant life either as zombies have a bit of that je ne sais quoi as well, with epic traffic cone helmet defenses, pole vaulting track stars, and newspaper shielded businessmen (with no pants).

The undead assault starts gradually early on, as players build up their defenses using the sole resource of sunlight. Periodically, little suns appear on-screen that must be picked up via a simple tap. However, in order to garner more sun, players must build a resource-producing plant – Sunflowers. Obviously, this will cost sunlight as well, so the game quickly becomes a challenge in determining what to build, where, and when. Moreover, there are only so many places plants can be put, thus deepening choices further (eventually you can dig them up and replace them). This is further topped off with the fact that decisions need to be both quick and thoughtful, because the zombie waves ramp up very quickly and it is very easy for your plants to be eaten and overrun.

Visually, the style of this app is just as fantastic as its creative character designs with each plant holding a vicious, yet cute, Mario-like art style, while zombies have this perfect, dimwitted, yet try-hard attitude about them. Heck, even the help menu is an amusing letter written in zombie’ish handwriting stating the player wins by letting the zombies reach their house. Even the sound effects compliment themselves perfectly to this zany, cartoon style.

Unfortunately, there is one significant letdown. Despite the fact that Plants vs. Zombies exemplify what an iPhone game should be, it easily falls on our list of games that should have Facebook Connect. Granted, the game does have extremely amusing achievements built into it, such as “Don’t Pea in the Pool,” but it’s just not the same without being able to post it to a feed. With the massive amount of potential strategies, layouts, and mini-games (i.e. bowling for zombies with Crazy Dave), this is an app that screams for social features.

Nonetheless, the franchise is not without some social hope as fans of the game can at least go onto the Plants vs. Zombies website and create a nifty Zombatar (a zombie avatar) for use on their various social networking accounts. Facebook, Twitter, and scaring your mother are what comes recommended.

Of course, the lack of Facebook Connect is hardly enough to keep us from playing Plants vs. Zombies. In fact, it’s hardly been enough to keep over 300,000 from playing. Just today, PopCap actually announced, that within the first nine days of availability, Plants vs. Zombies has sold over 300,000 units (at $2.99). The game reached #1 in the App Store within 24 hours and has since grossed over $1 million. This has made the launch the top-grossing iPhone launch ever in its history. To top it off, it is now #1 in over 20 countries, including Canada, China, Russia, Australia, Germany, Denmark, Ireland, and Norway.

In the end, Plants vs. Zombies is a very wise $3 investment for any iPhone or iPod Touch owner. That said, we look forward to seeing more from the folks over at PopCap Games, and hopefully, a Facebook Connect announcement in the future of this already excellent game.