Plants vs. Zombies is a tower defense game for Windows (also available for Mac OS X). The game challenges you with a task of stopping a zombie invasion: your garden is the last line of defense against zombies, and you need to use given plants to stop them (they really are able to).
Unlike other tower defense games, the enemies advance in a straight line and you can't modify their path. You can only shoot them down with different plants. The first plant that you get is the pea plant, which shoots peas at zombies. Afterwards, you get credits to seed new plants by harvesting the power of the sun (by clicking on the little suns that come down from the sky). Those give you 25 credits each. You can also plant certain plants that will give you credits throughout the levels.
In general, it all boils down to having enough credits to get shooting plants and slow the zombies down with whatever means necessary. Also, as the levels progress, the enemies become harder to kill, so you have to adjust your technique quite a bit.
Graphically, the game is nothing to phone home about, but the graphics are quite nice and everything goes down smoothly. The game installs really quick and loading times are pretty much next to immediate. Plants Vs. Zombies should prove fun and addictive for all ages. It is not a game with a lot of gameplay depth, but it works great for killing time.