Prior interest: high
Of the first round of WiiWare demos, the World of Goo was the only game I'd previously played as it had been released with a demo on PC. Thanks to gushing reviews and a few minutes with the demo, I was already interested in the game. In addition, the publisher (2D Boy) gave away the soundtrack, which I always appreciate. Since then, they posted some thoughts on game design and sold the PC version of the game for, well, whatever you feel like paying. So they have a lot of my goodwill if not my money. The only question I had was if the WiiWare version would be a better choice.
Odds of purchase: high
World of Goo uses pointer control exclusively, which limits the potential platforms for it. On the PC, there is just one pointer: the mouse. The Wii has the ability to display up to 4 pointers using the Wiimote, which ought to be used more often by game designers. Super Mario Galaxy's coop play is a bit silly, but giving the second player an onscreen pointer turns out to be both useful and clever. World of Goo on WiiWare runs with the idea in that 4 players can grab Goo Balls and add to the structure all at once. For some levels, like the giant tumbler level that requires throwing up a tower quickly before the floor moves out from under you, the extra hands are very useful.
Ultimately, the multi-player option is likely to be the reason I'd buy this game. On the PC, it's a fun diversion. The demo shows off some of the game's tricks and certainly leaves me wanting more, but on the PC I'll just move onto one of hundreds of demo or adware puzzle games that proliferate on the internet. But the same game with another pointer or three turns into a community experience. For now, the demo can be pulled out when the family tires of bowling and tennis and eventually, someone will want to do more than just play the first few levels over and over.