I really enjoyed the mood of this game. Others have suggested some audio, and while a few sound effects would be nice to have, I don't mind the silence.
The color palette is really striking and definitely helps to set the tone for the different worlds you see. Red is used really well here. Also, the font is quite good for this small screen size.
I haven't finished the game but I'm looking forward to exploring all over. You mentioned that the visuals had to be mostly symbolic, but I think that's a major part of what makes this game intriguing.