just, in this particular case, you need to remove from name all what is not a number:
dir c:\\test\\pstest | sort {[int]($_.name-replace "\\..*")}
the same result will be if you change the regular season like this:
dir c:\\test\\pstest | sort {[int]($_.name-replace "\\D")}
when you change the file naming scheme, the regular season, too, will need to change.
and to sort in reverse order sort-object is the key-descending. just add it to the end of the row.