I watched some tutorials on youtube about acrylic painting and mediums, but I realize that I still need a lot of work with the medium.

This is a painting of a blue crayfish. The inspiration for this piece came about during my walk home from school last week. As I was walking by a creek, I saw many disembodied, blue crayfish claws (they literally lined the bank of the creek). Being the benthic macro-invertebrate lover that I am, I painted this as a tribute to those poor crayfish. :C
Anyway, I really want you to tear apart this piece. I don't care how mean you are, I can handle harsh criticism.
Things that I have questions on right off the bat:
Should I leave the background flat? Or should I build it up?
I was thinking of including opaque bubbles in the background, should I?
How are my values on the crayfish? Should I make my darks darker?
Thanks in advance!!
