They are competent studies on solids, the cube is better, the sphere needs work. You might want to experiment with different light positions for the cube, and also with different alignments, like front aligned cubes, or trimetric perspectives.
As for the sphere, the shading cells are a bit too many and too evenly spaced I believe. If you were aiming to keep a matching material with the cube, it would be best to have less bands, two larger areas for a light and a dark shade at most, a highlight and, perhaps, if you are looking for a challenge, a terminator, but that is not so easy to tackle with pixels. Look for references on spherical shading on art guides, spherical objects on your house, and maybe even rendered "toonshaded" 3d meshes on google to get a feeling of how spheres are typically made on pixel art.