The exploration in this was so good! I felt like I could just get distracted by every new path I saw, and find something neat when I go down it. \(^o^)/ Though, I found it really difficult to keep track of where I've been and how places are connected, especially after the 4th marble.
The music was amazing too! I think my favorite track was the Caldera's BGM, and second place is the Ruins'. (^^)
This might be a weird criticism, but I think there could've been a bit more excitement? ｢( • ﾍ •) I don't mean more "action", it's more like... some mind-blowing discoveries or connections would have really pumped up the experience. The closest moment for that feeling was when I (spoiler!) froze some big pools with the Ice Ball.
My favorite thing about the game is the ways the different marbles interact with different environmental objects. It was always a joy to see it happen, and then go "Oooooh, of course that's how X would work with Y, why didn't I see that coming?" (◉ o ◉ )
All the different ways to interact with "basic" Water was so cool. The surprises even kept up all the way to the end, with what happens when the last marble falls too far. Pfhahaha, Of course it would do that! (^o^)
Nice game!
p.s. The big goofy eyes are so good. XD