Nice game - it feels like it would work really well on mobile and it kept me playing until I lost. One thing I'd say (though maybe you've already done this to some extent) - is manipulate the rng a little so that it can't spawn too many of the same piece - I think when I lost every piece on the board had a left-side line on it, so there was no way to combine anything and no way to avoid losing.
Still a really cool game with great polish though, and an interesting geometric twist on this style of game!