You've got to love Double Fine. They develop some of the most unique games around. Who else has made a puzzle game about Russian dolls? No one, that's who - not like Stacking, at least.
In Stacking, you play as little Charlie Blackmore - the smallest Russian doll around, and you solve puzzles by 'stacking' in to bigger dolls and using their special abilities. For example, you can stack in to a grizzly bear doll and use its growl ability to scare other dolls. A bigger doll might have the ability to perform an uppercut, which aside from physically abusing the other inhabitants of the world, also has puzzle-solving uses.
Abilities sometimes have to be rapidly combined as well. So for example you might need to use one doll to squeeze out a guff, and then hop in to another that can light a flame to cause an explosion.
Most, if not all, puzzles have multiple solutions and each levels has its own 'Hijinks' which ask you to get up to no good by doing five of this and ten of that, and what not, so there's plenty to keep gamers shuffling around.