World of Goo is a rather new game for PC and WiiWare ($20 on PC, 1,500 Wii Points on WiiWare), and will soon be on Steam. It's been out for almost a week now, but I haven't read a single bad review yet. IGN gave the WiiWare version a 9.7, and RPS recommended it very much, and WiiWare World gave it a 10/10. I had preordered it, and as such, beat the game the day it came out. I very much enjoyed it, and the 'story' (if you can call it that) and levels were very well done. They could have just said "no, that would be too much work" on many levels, but they decided to do them anyways. In my opinion, it's definitely worth checking out.
A demo was released today, and contains one chapter of the whole game (in the full game, there are 5 in all, with 5 being 3 levels long, the others much longer).
tl;dr, everyone likes it and you should try the demo.