Scary, adorable monsters are attacking your castle, and the only way to defend yourself is to match them together, puzzle/strategy-style. Your goal is to defeat enough enemies to advance to the next level. To maneuver them together, you have to destroy blocks of landscape. Click on any group of three or more tiles to make them disappear, allowing more mountains, grassland, crops, gold, and creatures to fall in from the top. Once you have a group of two or more monsters, click on it to eliminate them.
If a bad guy reaches the bottom of the screen, it damages your castle and leaves. If a pile of gold reaches the bottom, it adds to your wealth, which you can spend between levels on upgrades.
On later levels, the monsters get stronger and tougher. They arrive in greater numbers, do more damage to your castle, and must form larger groups before they are vulnerable. This gradual evolution of threat and the light customization (I like the upgrade that converts crops to gold) gives Puzzle Defence a little strategic oomph, but really it's just a pleasant way to spend 20 or 30 minutes. The sound design passes the Crunch Thump Crunch Thump likability test, and I generally just want to hug the game and tousle its hair. I'd love to see a fleshed-out sequel.