In World of Goo, your primary objective in each level is to build structures out of balls of goo (blobs that connect to each other when placed correctly), and eventually get a tip of the structure to a pipe that sucks excess goo balls in. Each level has a certain amount of goo balls that you have to collect to pass, so even getting the structure to the pipe will not guarantee victory. There are no enemies in the game, but your environment plays a deadly role, making you dodge spikes, spinning blades, wobbly precipices, and even fire. In each level, you must find a way to best traverse the terrain in order to get to the pipe, which is easier said than done in most levels. Goo balls come in many varieties, and are slowly introduced even towards the end of the game. Their appearance, function, and uses are varied, and examples include retachable, flammable, albino, "dead", balloon, and many more.
The art style is reminescent of Worms Armageddon, the music, of Katamari Damacy (but better!), and the gameplay is, well, just plain solid. Rarely do you get such a polished game even from large developers. Each part of the design of World of Goo just seems finished; everything is alive and interactive, the sound effects are highly varied even for the litttlest motions. Goo balls splatter and squelch, and even react to friction. Menu screens are highly animated, and the music pervades the game with awesomeness.