Everyone knows the best part of a sandwich cookie is the filling. If Nabisco would sell a tube of the sugary white paste that they pump inside each Oreo, they could make a killing (or just a lot of cavities).
Just Fillin' gives you the unadulterated good stuff: pure puzzle gameplay without any fuss or fringe. There's a massive cavity that needs to be filled with modes, but that only highlights how sweet the game is.
Your job is to displace a pool of water resting along the bottom of the screen. Just Fillin' gives you one tool in which to do this: your finger.