A fun, but short, game indeed! The current button set up is interesting, but here's my suggestion.
Rotate: As someone else mentioned, maybe tie the camera the Right Analog stick, it's what I automatically went for.
Locking: Y is doable, but give that option to the Right Analog stick by clicking it down.
Attack: Try linking it to the LT Trigger button, it feels more natural than "X".
Regarding sounds, its seemed alright, however the creature growling/screaming between stages was very loud, it made my headphones pop. Let me tell you, these babies aren't cheap, so for the sound that you used to do that means it needs some tweaking.
Boss suggestion: When the rocks begin to fall, have the shadows expand from nothing to their full size as the rock approach, it feel odd to see shadows appear everywhere suddently and somewhat takes away the feel of urgency vs seeing the shadows slowly increase in size incdicating they're getting closer and you need to hurry.
Those are my main suggestions, if you have any follow up questions, let me know, and I'll answer them to the best of my knowledge.