Really solid puzzle game. Had to stop at lvl 14 since my brain stopped braining and I was stuck for 15 mins. Will come back later and finish it.
I really have no feedback, most of the features are already polished and the design of the game was really well thought. I admire the way you have integrated levels into teaching player regarding the new tiles. I learned some new things playing this regarding how to develop games.
Kudos for a great game!!
Have a nice day :D