If you have tried Dreams, I would recommend Little Big Planet. It has a game builder that is a step down from Dreams but they were both designed by the same company, Media Molecule. Not to mention LBP is just a magical game all around!
I came into this thread with the intention of recommending LBP and possibly Dreams, although the latter is a big step up in complexity. LBP lets you do wonderful, creative things in 2.5D without any coding knowledge.
But seeing GBG being mentioned, I wish I had that growing up. Looks like the perfect way to get started.
