Nice start! A couple things jump out at me. The background just being a resized and palette-swapped version of the foreground makes the whole thing look monotonous. Try a different texture for the background, such as the square blocks. Also, your rock tile looks good on its own, but when you actually use it in an environment, it looks weird because the lighting is flat. Try shadowing the undersides of big rock clusters so it actually looks like a chunk of rock. I also think you could integrate the squares in better with the rocks, like have the edges of the rock go into the square tiles more.