apply a slight noise effect to the terrain with the noise brush, on almost minimal settings and it will make it look 100 times better.
As pointed out textures in any engine, look bad when they are flat and rely only on the normal map, and the angle approaches a full 90 degrees.
Challenge is normal just tells light where to be, it doesn't change a flat surface, and anytime you hit 90 degrees light data becomes really thin. As light tends to bounce not roll along a surface.