This first thing i noticed is (and i think this is the big thing to fix if you have time), there really is no definition between the foreground, mid-ground, and background. Separate then add some interest to the silhouettes of the composition.
The second biggest thing is, the plants are too saturated. Unless this is the style you're going for, use the desaturation node in the MAT Editor and desaturate all the plants by at least 0.25.
The last thing is, beyond the last big tree in the middle, there really is nothing going on. Add some plants that you already have made back there to add some depth.
All things considered, this project is coming together well. I was nervous for you when it was just the hills with no plants of rocks; but you set-dressed it nicely. Keep it up.
