This is an odd game. From the Start screen, you can select the first world, which I guess will be the only one available in the Demo. You start off with the first level, Going Up, also titled Easy As Goo Pie, and you already get to learn what the game is like. Basically, there's a structure made of goo, with axis and points. What you have to do is grab one of those points with the Wii Remote and then go a little higher, while still holding the point. Basically, this will create more axis, and the structure will grow. You must keep doing that until the goo reaches a pipe located higher.
When the structure reaches the pipe, many blobs of goo (with eyes, yuck!) climb up into the pipe, and then you get the results. For every level, you have to have an amount of blobs go into the pipe, and if you have less than the required amount, you lose. If I understand correctly, your amount of moves is limited by the number of living balls of goo on the structure. Every time you add to the structure, you need to use one of the balls of goo that is passing by on an axis. At the end of a level, the game calculates the number of goo balls that were still on the structure when it reached the pipe.
In the third level, you're introduced to sleeping balls of goo; a whole lot of them. You need to go pick them up using the existing structure and the goo balls on it to wake them up, and then climb up to the pipe once more.
Basically, this is a structure puzzle game like the ones where you have to build a bridge, except it restricts the amount of points you can add. The extra balls you collect in every level are added to a a special mode called World Of Goo Corporation, in which you must try to build the highest pile out of those extra balls of goo.
Further levels available in the Demo version add even more features, such as enemy cogs destroying structures, time insects that you can click to undo your last move, red goo balls that float (Oh yes. They float. They all float down here.), and other stuff.
Personally? The first few levels were fine, but I didn't like the game as a whole. It's just not my thing. The levels in the demo get extremely difficult, and I think it's too difficult for a demo. Every game has to walk the fine line between easy and hard, and this game took a step on the “hard” side. Maybe it's the type of puzzle that isn't for me. That's possible. Either way, I did not really enjoy the demo, though I admit it's a good basic idea. It could have been fun, but I guess it just isn't for me. But if you think you'd disagree, well, the demo is still on the Wii Shop Channel, so give it a try.