First the praise, the roofs and hedges and rockiness are done quite well, I certainly can't do that, and I think that I see three levels...I can see two for sure. Thinner lines and smaller houses is good but you might want to erase some detail the lower things get...farther away = less detail so exaggerate that. A good cue for the eye would be to add some shadows, bigger shadows at top smaller shadows lower...that might help fool the eye into enhancing the perspective. Some subtle gray tones in the rocks might also go a long way without having to do hatching and cross-hatching...darker tones and more detail for things close and lighter tones less detail further away. This could be something stellar if you work it a little bit more, quite nice as is, though.