Plants vs. Zombies
There's a demo on Steam which allows you to play the game free for 60 minutes. It's one of the better things you can do with 60 minutes of your life.
Plants vs. Zombies is a tower defense game from PopCap. Yes, this rang alarm bells for me, too. Low-budget? Undoubtedly. Simple? Sort of.
It starts out slow; the first several levels really ease you into the gameplay. Ten minutes in, I felt a little bored, and started wondering what all the fuss was about. But in these first few stages, the game is disarmingly easy, and inoffensive enough that I simply preferred to keep playing over stopping.
Then the challenge kicked in. Ideal plant placement is initially not difficult to figure out, but it gets more complicated when you gain more plants, and have to choose which ones to bring into a level with you. New enemy types force you to rethink your strategy. And then it gets dark, and the sun-powered resource system is appended with magic mushrooms and shit.
The brilliance of Plants vs. Zombies is that, although it is a simple game at first, it doesn't stay that way. This is real, good, old-school game design - start basic and keep building. Almost every level introduces a brand new element, be it a new plant, a new zombie type, or a new playing method: some levels completely throw out the strategy and resource management for pure arcade-style action. The levels that don't, will instead tweak the game's vital variables like zombie count and swarm rate, so the experience always has a fresh element of challenge.
Which is not to say that the game, at least as far as my trial went, is ball-bustingly difficult. I never died, and rarely lost any plants. But even though I was always one step ahead of the zombies, they kept pace pretty well, and I have a feeling that later parts of the game (I got to level 14 of 50) will be less easily trampled.
Though the game supposedly retails for $20, it's $10 at this very moment on Steam. Andrew Jackson is a bit iffy about the game, but Hamilton is all over this bitch.
Progress: Level 2-4