This is a really cool concept! It's visually very put together as well, although at times it can be hard to see the shape you're supposed to fill if it's right near the center.
I do think it would be cool to have more things change besides the speed of each shape in terms of difficulty scaling. If you work on this in the future adding more blocks to the snake's length and having more complex and larger shapes could be a fun way to do this. As it stands once you get the hang of the mechanics it kinda falls into the same trap other snake games fall into (runs start really slow and take a while to get to the fun part, and the higher difficulty gameplay is still essentially the same as the early game).
However, like snake, I do think this is a variation I would find myself coming back to every once and awhile as is, so great job!