By focusing foremost on solid game design over more superficial concerns, World of Goo perfectly exemplifies a lesson even the best AAA developers occasionally lose sight of: In order to really reach for greatness, you have to start with a strong foundation.
Bottom line: World of Goo is the most charming, creative and generally weird indie title to come out this year, Braid included.
Recommendation: If you're an obsessive completist, pick it up for the PC for mouse support. Otherwise, grab it on WiiWare. Either way, it's a must-own.