I like it, but it seems a little bit flat.

The truck is pretty good, although the barrel of the gun seems to bend downward. The clouds look more like oekaki than pixel art, especially the bottoms of them. Try cleaning them up a bit so they won't be as rough.

I think what I really like about this is the color choice. The sky and clouds are very nicely colored. Still, you used 43 colors and definitely could have done this with less.