I assumed that it's night time, given that the sky is so much lighter than the landscape but is still kind of dim itself. Maybe not? Sorry I reread the OP and saw they are clouds. Hmmm.... Honestly I would try cutting them, replacing that area with a landscape/horizon and just having smaller clouds actually floating within the sky. These will be much less ambiguous. That's just my take on it.
Either way, yeah there is a lighting mismatch. Of course, given that we can
see the sun/moon in the background, all those surfaces facing us would actually be in shadow, but that isn't really practical for game graphics.
Aside from that, the scene looks pretty good. One thing that bothers me is the dark gravelly ground you have blends quite a bit into the background. I suggest highlighting the perimeter of it so it's very clear where the player can walk (assuming you're meant to walk on that? If not, you need to lower its contrast).
The other thing is the large horizontal divide created by the clouds/sky is quite distracting. It keeps distracting my eye away from the actual play area. Remedies include shifting the line up/down in the scene (I'd suggest up) to make the play area take up more of the screen space, OR lower the contrast of the background. You could do that by making the sky the brightest tone and the clouds the second brightest. This will destroy your sun/moon, but that was creating a lighting conflict anyway, right?
Just some thoughts. Also, welcome to Pixelation