Looks very nice, although on the second one especially I would darken/size up the shadows a bit as their hard to see against the flat grey background and thus give the impression of floating a bit too much. You also want to watch sizes vs vertical position on the landscape. It's a human tendancy to think that the further up something is, the further away it is, so when you have no plain background, the sizes are kind of confusing and misleading, you might consider playing around with those. (For example, don't think you meant this, but the basi in front looks hueg, which could be a nice effect.
Also, the human's hair in the second.
I like them a lot, keep up the good work, and maybe some other backgrounds could like nice.