The main criticism I'd give this game is that the volcano world feels a little uneven, compared to the first three worlds. A few select volcano stages (4-12 and 4-14 especially) were mostly just frustrating, and disrupted the "flow state" created by the first three worlds. Not even to say they were impossibly difficult; they were just a little annoying and felt out of place. Especially when I cleared the other 80% of the volcano stages in 1-3 attempts.
Besides that, this is a really fun little game. You created a lot of really good gameplay from a very simple mechanic! I really enjoyed the first three worlds, and I thought their levels were well-designed. I like that each world has a different set of mechanics, and it's all tutorialized well. (Particularly liked the water in Atlantis being used as conveyor belts with a twist.)
Very nice work on this one!