It looks very unrealistic and kinda lame.
There is no tile variation, and why the hell did you use cobbles? Use rough dirt and dirt and maybe a bit of rock.
As for the black stones, try to think about the variations you are using and pick the larger, fatter, more solid boulders. Also, lower the rocks so those 2D pebbles don't show. Furthermore, you might want to place the rocks closer together and in clumps or piles, rather than like they are now.
The brown rocks just don't fit. Get rid of them.