The Drude model contained some very extreme simplifications and
estimations. For example, the lack of quantum mechanics, and the
fact that the electron number density approaches the limit where
the gas cannot be approximated as an ideal gas.
However, even with these gross over-simplifications, the Drude
Model was quite successful at explaining a number of observed
phenomena of metals, as noted in the slide above. This is a tribute
for the general success for the search for simple physical models
to explain more complex detailed phenomena.
It is remarkable that such a simple model had such widespread
successes, even with the acknowledgement of many of it's
shortcomings.
