I don't know about this..
It looks like the pillowshading was intentional, and because of it, everything looks bad. This, and coupled with the black lines all over the structures, make them look worse, if not awful. It also makes it hard to identify the lightsource, like those GYMs; they look as if one was viewing them from a frontal perspective, instead of a top-down one.
Dithering just worsens up the lot of them, if it doesn't fix them.
Let me explain something to you. Pillowshading, as we know it, is a horrible shading style derived from the lowest depths of hell, brought to the world to bring doom to anything calling itself a sprite. It's lightsource is located between the viewer and the object, which gives this undesired feel to the object being shaded. It's actually be the bane of any spriter looking to improve.
I would naturally go and suggest you to remove it all and look for better style, yet, you seem to have almost EVERYTHING covered in it, which leads me to conclude that it must be a style of yours or some sort, and thus, I can't help much here.
If not removing the pillowshading, I'd suggest you to at least remove most unessesary black lines inside structures and buildings, as they look ugly and stand out much, much more than the areas they cover. Shadowy areas should still keep the blacks around.
Another thing, the water tiles, some trees and the grass look extremely grainy to the point of failure, and some of them are also pillowshaded. Maybe if you smoothed them out, they would look a tad better. I'd say give it a try.
The house looks smooth and well done though, but the excessive dithering gives it a scratchy, rather bad look.
You see, one thing I liked about this was the designs you used, like the GYMs and the pyramids.. They look awesome. If you just could fix up the shading it would look loads better, if not perfect.
Ah y claro, si nesesitas una ayuda o algo, mandate un mensaje. Ahi podre dar mas detalles.