Cool little game, kind of like 2048 crossed with Tetris! Very satisfying when you can get a chain reaction going.
I like how the UI at the bottom simultaneously shows you what the next shape is going to be, and also shows you the "order" that the shapes merge in.
I think my suggestion would be to make the colours follow a specific pattern, rather than being seemingly random. I see that the number of sides of the shape corresponds with the order, but the colours is what I notice first.