This was a fun little puzzle game. You did a decent job with the level progression, though I think you might have benefited from having a few more levels to help slowly introduce some of the concepts. For example, you could have a level between 3 and 4 where you introduce the water tiles with a slightly easier puzzle. A few more levels at the end, once you’ve introduced all your concepts would be fun as well. I was having fun and would have enjoyed more.
The timer option was a nice touch. I liked that it was off by default, so that the base game has a slightly more laid back feeling while still giving you an in-game ability to see how long it took you to do any given puzzle. It was also nice that the game kept track of the time, even if you didn’t have the timer active, so you could go back and see your highest scores afterwards.
I think you have a good base here and that it has potential for more.