I do quite like the mood of the game, the soundscape is relaxing and creates a somber atmosphere.
I wasn't able to find the last shard, even after resorting to a grid search. Consider adding some hint/cue that indicates when a shard is close, so the player knows where to focus their efforts.
What about something like a 'shine' SFX loop that pans from ear to ear based on it's location to the player?