I see that you're going for a more stylized look for the rock formations, but your rocks come across as chips or fragments of glass or something in the dirt.
You've got to be clear what your forms represent -- even abstract games like Kirby's Superstar and Super Mario World (or even Lttp Zelda and other RPG's w/fantasy worlds) make sure the forms clearly represent something three-dimensional, despite them being clearly abstract and nothing like what we see day to day in our world -- that is... with the exception of form or color.
Right now, your color is similar to real-world dirt/mud in your 'rocks', but your form doesn't represent any sense of three-dimensionality, whether or not your 'rocks' should eventually look, form-wise, like real rocks. I suggest adding at least another color to it to hint at three-dimensionality in the rocks. That's the only reason your grass works after all -- it has another color you can use to shape forms with.
If you don't want to add another color (which isn't usually the best option imo -- maybe even in this case too), you can make the lighting resemble the lighting on rocks/mud a little more by removing the straight/sharp edges and clear triangular features, essentially succumbing to the fact that you are simply making mud/rock and nothing more spectacular, otherworldly, or exotic.
That aside, you could consider weaving some grass or vines into the cracks in the forms along the edges if you'd like to add variation. Other than that, your hud should stand out a little better than it does (i.e. increase its brightness of the hearts, outline the hearts, add a panel behind the hearts, draw some decorative stuff around the edges of the hud like in The Illusion of Gaia/Time, etc. etc.)
