Thanks for the feedback! I agree with the compositional comments.
Everything looks very pleasing and nice to look, it is rendered well. But I'll echo king_bobston's statements about the cloud-tree relationship, the placement hurts the composition.
- I would of attached the tree to the hill, but the tree's leaves and the background look nice. -
I really like the folliage but the way the clouds just peak a bit outside of the tree is bothering me composition wise, hard to explain. I would position the cloud differently, not sure where. One solution would be to decenter the tree and move the clouds to the other side, like tree left and clouds. A probably better one would be to make the hights of the cloud peak left and right, instead of the center.
Only other thing bothering me is the tree trunk being cut off at the bottom, like felchqueen said. I also think that the very round grass (not that you get me wrong, problem is tree trunk, not grass) adds to make it look wierd.
Did I say that I like the folliage? I really like the folliage. Gives a nice feel for depth. The other textures are great, too.
Nice pixeling, but the perspective seems a bit off to me (tree from front, hills from higher perspective).
Lovely clouds and leaves, I think if the tree was moved higher (or you pixeled a bit lower) the trunk wouldn't look so flat, our brains are missing the vital bit to give it volume.
nice grass, nice gradient, nice lighting... lovely skies and leaf !!
not a fan of simple tree but this is very artistic 
Amazing stuff! It's going to take a looong time to finish your game if the sprites are this complex :O.