Rather surprised that nobody has mentioned Rule 16 of the Rules of the Air - aircraft shall conform to the pattern formed by other aircraft etc,
Also landing priority - when two aircraft are approaching to land the lower has priority....except that you should not cut in front of an aircraft which is already established on final. (emergencies excepted).
What worries me are the aircraft that call an A/G and ask things like "Am I clear to join left base, straight in etc?" - they dont seem to understand that A/G cannot issue such a clearance.
As for the overhead join - subject to any local noise abatement - there is no problem with this so long as pilots know how to fly it and is indeed the correct way of joining the circuit at an uncontrolled aerodrome (my comments relate to UK only - our cousins elsewhere have their own way of doing things!).
Also notwithstanding basic airmanship if you are in the ATZ and someone joins "Long Final" then they are OUTSIDE the ATZ so you are quite entitled to turn in ahead of them!
At times I am quite appalled at some of the circuit discipline (or lack of it) which is displayed by some (usually visiting) pilots.