Given the canvas size (40x40), I'm pretty sure it is safe to say that it would of been in your best interest to work on a larger scale so that a proper dithering method could have been implemented. As it currently stands, all I see is skewed white pixels on a black background that barely holds shape to scenery. Proper dithering becomes more of a necessity when you use minimal colours, as does the size of the canvas sprited on. You just need to learn how to use the basic background colour to your advantage when meshing the primary detail colour in two toned sprites.

well you've chosen a landscape using 2 colours, unless your a dithering expert I'd simplify things,  it just isn't working for me at all. I'd probably also work a bit bigger than 40x40, it wont do this any justice..