IMO the gameplay idea have potential, but the fact that the player can switch shape at will makes most obstacles pointless (doors, buttons, breakable walls etc.) as the player just has to switch to the right shape. No thinking required.
Easiest way to fix the gameplay would have been to switch shape when walking on something. With this and your already existing mechanics it would have been possible to design interesting puzzles.
Otherwise, visuals and audio are simple but work well together. And the flatland-inspired world fits the theme perfectly.