Fun 3D building software?

I'm looking for a quick and fun program to mess around with. I mean a program with pre-set graphic objects that you can import into a scene and mess around with.

For example some Lego blocks game. Something with virtually no learning curve, just drag and drop fun.

 

Sketchup is too complicated, it's also an architectual program. I guess what I'm looking for is more of a game than a program, and more than likely doesn't exist on Mac