This arrangement provides metals with many of their characteristic physical properties. The shiny luster is because with so many free electrons, and only two each in a given energy level, then the electrons form wide band of low energy, with the magnitude of the energy of the order of visible light. The electrons easily absorb light and re-emit it right back again, with no loss or gain of energy. This is the origin of the metallic luster. Metals can conduct electrons easily because the electrons are not localized in the crystal.
Metals are malleable.
This is because the atoms can easily rearrange themselves in the sea of electrons. Covalent Covalent bonds often form between atoms with too many electrons in their valence shells to give away, but not enough to easily fill. Thus they share electrons with their neighbors, in such a way that including the shared electrons the shells are full. These are stronger bonds than either of the other two types. This is because the electrons are shared.