I think this could use better foreground/background separation. I'm not really a fan of how the colors you chose are mostly super-saturated, and the daytime sky in particular is hell on the eyes. The sun looks kind of odd as well - the green AA doesn't look right to me. Nice readability for such small tile sizes though.

2 extra points for minecraft and that you tried to go as humanly small as possible.

I like your choice of colors EXCEPT the nightsky which should be blue and not a pure grey imho.

Also, the clouds really do not work as lines in this small size. Overall, very nice idea and it certainly has the "minecraft" feel to it. Keep it up!