the Molecube takes the challenge to the next level. You must twist the puzzle so that each of the nine colors appear on all sides - kind of like a 3-dimensional Sudoku puzzle - not all one color on each side like a regular twisty puzzle. Don't be fooled -- the smooth, colorful little balls feel great in your hands and move smoothly almost like the real protons and neutrons might in the center of an atom. It's super fun to fidget with, but really hard to solve! 4.5 out of 5 Difficulty.