There is some great progress here, but I thought I would throw out a through things that came to mind. I would push dark's especially in the sky a lot more to make the tree pop and dark the tree in the foreground to make the center focal point stand out even more. As was previously mentioned the way to make something brighter is to make everything else around it darker (there is more to it than that but its a good rule)
I would redesign the rabbits if possible as Lee White mentioned, they are too similar the to trees and they would look much better if the shapes were somewhat opposite or at least different to the trees. I feel like they get lost in the design when they are not meant to (I am designing a creature that looks similar to it's surrounds because of the theme, but the ears in yours seem to be an afterthought or somewhat obstructive to the piece)
As Lee said, if it's getting too stressful then switch to some other piece for a while and come back and look at it with fresh eyes. I have a few pieces that have been put on hold because of that, but you will learn from your other work and that will help you when you come back to the pieces you dreaded. Hope that's of some help :D
You are doing some great work though Eric and I you definitely have the power to push on to learn more!!