Bond Type of Lead: Metallic or Network Covalent?
As you proceed down Group 14 the metallic bonding structure tends to become more stable than the tetrahedrally bonded structure we see in diamond, Si and Ge.  Tin is actually a transitional case.  At typical room temperature it is metallic (white tin) but upon chilling it transforms to the tetrahedral allotrope (gray tin).  By the time we get to lead we have fully gone over to the metallic phase.  

Because the tetrahedral bonding structure requires each atom to contribute four valence electrons, this tetrahedral --> metallic transition may be seen as a form of the "inert pair" effect that emerges in heavy atoms.