Does this decision keep cities from essentially regulating firearms ownership to the point that ownership is essentially impossible for the average person?
I would say that the court acknowledged that restrictions can remain in place but your right to own firearms is acknowledged. The court left open the right of cities (and states etc) to control ownership of certain kinds of firearms and restrict their carry.
2. Like most rights, the Second Amendment right is not unlimited.
It is not a right to keep and carry any weapon whatsoever in any
manner whatsoever and for whatever purpose: For example, concealed
weapons prohibitions have been upheld under the Amendment
or state analogues. The Court’s opinion should not be taken to cast
doubt on longstanding prohibitions on the possession of firearms by
felons and the mentally ill, or laws forbidding the carrying of firearms
in sensitive places such as schools and government buildings, or
laws imposing conditions and qualifications on the commercial sale of
arms. Miller’s holding that the sorts of weapons protected are those
“in common use at the time” finds support in the historical tradition
of prohibiting the carrying of dangerous and unusual weapons.
Pp. 54–56.