Stop the undead with your gardening skills!
Plants vs. Zombies is a classic tower defense game created by PopCap in 2009. You must defend your home against a legion of undead, with only your gardening skills to save you!
As this game was a critical success, there's probably not much I can say that hasn't already been said about it. Instead, I'd like to mention my reasons for why it's such a great game and what made it so successful.
For starters, PvZ has a colorful and family-friendly art style, which is atypical for any game containing zombies. When you think about it, a dark and gory version of this title really wouldn't make much sense anyway. Plants make for a brilliant choice against the zombies here, as it increases the appeal of the game even more.
In terms of game play, it features a fantastic learning curve. Introducing new plants in the form of rewards at the end of most levels provides that feeling of accomplishment while also piquing the player's curiosity. Most times, the following level is designed to showcase the strengths of the newly-gotten plant, making the majority of the game a continual and gradual tutorial. I have to think that the developers of PvZ took notice of Portal's design theory and adapted it for their game (also to great success).
The addition of mini-games, the Zen Garden and other goodies adds a little variety beyond Adventure mode and even gives players an incentive to play each day and collect rewards. Again, this wasn't a new idea by 2009, but incorporating it into PvZ (and indeed many other games) was a great way to keep players hooked.
So, if you haven't gotten Plants vs. Zombies by now, go grab it on Origin while it's available for free!