What's going on with the blue in the tiles? Make it clearer so the viewer can tell.
You would have a way nicer background if you used more than just 50% dither to blend. Spriteart has a good dither tutorial if you need one, or you could open MS paint in 1-bit mode and look at the palette swatches for ditherpatterns.
The dirt could use to be more brown and dirty looking than the yellow it is now, or if it's sand it could use less grass and more cunes with liffle tufts of plant life.