Like most great games, World of Goo gradually adds depth to its gameplay. The standard, black goo balls first introduce the basic structure types, but I played with several other creatures. Green balls form three arms -- so players need fewer to make large objects -- and they can also be re-used. Balloons automatically attached themselves to objects when I brought them near, lifting a group of hardened goo balls up to their goal. And more ball types arrive later in the game. For example, 2D Boy developers Kyle Gabler and Ron Carmel told me about the rotund beauty ball, which is too heavy to be lifted but can be prodded to the left or right.

The gameplay hooked me, but the terrific art, animation, and sounds complete the presentation. Goo balls are happy to please, eagerly hopping into the ominous pipes, squeaking and chirping with glee. This wry humor and style should lift the game above other downloadable competitors.

World of Goo will be released simultaneously for PC, Mac, and Linux alongside its WiiWare debut. Those computer editions will be nearly the same game, although only the Wii version will allow cooperative multiplayer. 2D Boy hadn't yet determined the number of people who can play at once, but at least two gamers will be able to point and position balls at the same time.

Look for World of Goo sometime this year, hopefully not to far from now.