First of all the tutorial is simple. The fact you use Label nodes on Godot is just a dumb but yet simple and efficient way to learn the player what he needs to do. The instructions were clear, and the gameplay very simple. It was also a very good thing to remove the tutorial when you completed it instead of going back to it.
The difficulty was hard, but the time was just what was needed for me. This water bar mechanic is again, very simple, and it fits the theme of Oasis very well in my opinion. The tilemap sprites were great...
So what I have to say: Simplicity is key and you did very well with this game design pillar, I wanted to restart until I complete the 3 levels of the game. Very cool game! :)