I really like this piece. It really makes me think because the top reminds me of the sky and the ground; but then below makes me think of underground and how much bigger the meaning could be. Even with your color scheme being limited to monotones, it is still full of different colors with mixed subtleties, adding on to the vision of the piece. As any art teacher would say, texture is important and you showed that here with varying textures all over; especially on the flower. My favorite particular item would be the tree and its roots. I love how intricate they are.
As for things to work on, as a whole I would say to continue to work on individual shapes. Just continue to work and make them even and intricate, not saying they completely are not, but continue to work at it. Some of the mushrooms and maybe the flower could use some more attention, however if their shape was deliberate, since this piece clearly has symbolism, keep them as you please.