Summary of Sommerfeld Theory

I am just trying to state some of the outcomes and drawbacks of the Sommerfeld theory. The Sommerfeld theory was useful to get the solution for the Schrodinger equation to get the allowed electronic states, Fermi-Dirac distribution was used to determine the population of states and the electron scattering (unknown mechanism) was also well explained. So the Sommerfeld theory was more helpful to give the better shape for the free electron model.
There were numbers of questions which were unanswered by the Sommerfled theory like; the true mechanism for the electron scattering, the unhindered motion of the conduction electrons in metal for the significant distance, the dominant contribution to the heat capacity of t he solid for T>=10K, and why only the positive charged particles are responsible for the electricity conduction in some metals?