
I'm sorry I can't help much with specifics, but here are at least some general impressions of this piece.
The landscape and objects are good and evocative. It's an image that you can get lost in looking for details and trying to recognize familiar shapes and objects.
But, as you state, there's something a bit off about the colours. Frankly, they're dull. And though the colour scheme is varied the overall impression is bleak. Sadly, I'm missing the right vocabulary regarding colour theory and such to put into words why I feel the piece fails in this aspect. However, I do feel that it all ultimately comes down to the way that the lighting is handled. For example, you could do a lot more with contrast between bright and dark. Let the light sources leave a stronger impact. Be bold with cast shadows and brightness variations within the same hue. For example, you have an obvious, big light source in the center of the image, but it's effects are downplayed. A setting sun should produce a very bright, yellow or orange-tinged light, while the shadows are very dark and have sharp outlines.
A minor thing that is distracting to me is the white glow you've applied to the edges of some shapes, namely in the bottom left and top right. The only purpose it seems so serve is to arbitrarily make some parts of the image blurry. It's also counter to the general style that the rest of the piece is made up of.
I hope these observations are of some use to you. I'm not sure my solutions are what's really needed. Heck, maybe they are contrary to what you are trying to achieve with the piece!
Anyway, good luck! I hope to see more.