I really like this for some reason. I find it soothing. 

Pretty good first piece, there is obviously careful pixel placement here =)

You could make the lines and shapes ('clusters') cleaner yet, giving more emphasis to the simple natural pixel angles (as you already did).

Colors could improve too: right now you make the classic mistake of separate 'color ramps', there are just 4 different hues coming in different values. Try some hue shifting instead, to build a more 'organic' palette.
The choices of distant mountain colors are a bit weird too, maybe you can make them work more assertively, or use more natural options like purplish blues.