Available for PC and through WiiWare (Nintendo's downloadable game service for the Wii console), WORLD OF GOO is composed of a series of physics-based puzzles that involve building bridges, towers, scaffolds, and other structures out of the game's titular material. The general goal is to move the goop toward pneumatic pipes strategically positioned within two-dimensional environments. These pipes suck up the goo and take it to the World of Goo Corporation, where it is processed into various products.

There are five chapters, each with over a dozen puzzles. When players aren't engaged in the story, they can head over to the World of Goo factory, where they can work with the bits of goop they have collected in an attempt to build the tallest possible tower. If you're connected to the Internet you'll be able to see goal marks representing other players' towers in the background.

World of Goo is a breath of fresh air in the 2008 video game season that has been overrun to some degree by guns and gore. The googly-eyed goo balls are undeniably endearing creatures, the colourful 2-D environments create a visually satisfying Dr. Seuss-meets-Edward Gorey sort of atmosphere, and the almost ethereal background music often sounds as though it has been pilfered from a Tim Burton film. Plus, the game's clever story about the World of Goo Corporation draws some vague but thoughtful parallels with real-world companies without ever becoming preachy about it.

But it's World of Goo's physics-based conundrums that make the game a truly special -- perhaps even brilliant -- interactive experience. Most puzzles have wonderfully imaginative premises. For example, one level set in a tumbler sends the player's tower falling to the side every couple of seconds. You have to be quick, strategic, and patient, waiting for just the right moments to attach your goo balls to a long, narrow structure that eventually wedges itself between the barrel's rotating sides. The key to all of this goopy fun is how the goo balls are governed by the same physical laws present in our world. All we really need do to solve each puzzle is apply our understanding of real-world forces such as gravity and wind. It makes for wonderfully intuitive play that has potential to appeal to just about anyone -- though later puzzles are tricky enough that they might prove off-putting to younger players. It's one of the best and most innovative games of the year, and it's dirt cheap, to boot.