I think it's quite boring and lumpy/ugly, and the palette doesn't harmonize well. The house on the left is my favourite. You should think of some more cool ideas to play with and really sell this game, as there isn't really anything here special or unique or particularly interesting.
Here are some random artworks which have inspired me. Pay attention to the palettes and composition of them, as well as the design features which make them interesting. Trying to shoot for a particular mood is one way to think about it - to keep focus, and keep things unified.
Feng Zhu
Flashback
Jeremy Fenske
Studio Gibley
Starcraft 2 (protoss mothership)