Right off, I'll admit that I got stuck at the first obstacle and didn't know what to do. Pressed the space bar waiting for the water to erode the hill so I could climb it. Silly me.
Anywho, I do love the concept of the game. However... [SPOILER]
Obviously there are some things you have to let go. It's fiction so whatever. A rock that comes to life and moves; ok. What must be a ton and a half rock climbing branches and nets on boats; sure why not. I had no problem with any of that. I thought the gameplay concept was new and a charming way to think about how to get around.
But the rock climbs down a volcano and blocks the only ventilation for the magma. Wait now, what? I think the other things I could let go because they were small devices to get the game moving. But the big thing, the climax so to speak, is sacrificing yourself to plug up a volcano. I get the sacrifice thing. But I think the physics of the volcano are important. Namely the part where the reason volcanoes erupt is because of overwhelming pressure in the magma chamber building up.
I read the comments and I realize this is an experiment but I implore you to think about the story concept a little more. I'm sure I might be the only one to have this problem (believe me I looked) but there's a difference between bending the rules as a plot device and saying, "This is how that works and that's all."
I also realize that the ending might not have been that important being that this game served another purpose, experimentation. The end may not have... well not have made sense, but everything else was great. The music fit nicely, the gameplay made you think, the animation was excellent for what it was, and even the story was good up to a point. (Ending would have been better if the game had a humorous vibe instead.)