Monument Valley is as close to the perfect puzzler that I've ever seen. At the beginning, I nearly gave up because it seemed a little too simple, but the beautiful visuals kept me playing, and it did get more difficult. The world that you control your character through is something of a 3D maze, but because it is isometric and has no perspective, various sections that seem to be at different heights end up matching up together. As the game becomes more complex, and twists like having the camera angle change can completely change the layout of the maze.
My favourite moment, when I knew I loved the game, was the level that involved a Penrose triangle (pictured). Said triangle is the perfect example of how something illustrated on an isomeric grid, with perfectly even lighting, could be impossible to construct "in real life".
Overall, I'd love to give the game a five-star rating, but I have one complaint: it's short. Rather short. There is an additional set of levels as an in-app purchase, but I don't plan on buying it as I fear its value won't be worth the cost.