Here is an ISIS fighter boasting that the air strikes are not militarily effective.
Sadly, he is probably right. ISIS is an army of militiamen operating is relatively small groups whose main armoured vehicles are pick up trucks turned into Mad Max style "technicals". Most supplies- and they dont need alot, are requisitioned from the locals (voluntarily, forcibly or coerced) and transported in individual civilian trucks. Likewise, there are not alot of easily demarcated front lines in the fighting.
As the similarily orgainized Serbs demonstrated in Kosovo, these types of forces mix in with civilians and can be very difficult to identify and stop. Then factor in that ISIS includes members who are veterans of both Iraq and Afghan conflicts who probably have a long list produced list of "dos and donts" produced by Darwinism when it comes to avoiding precision airstrikes.
In short, my guess is that effective air strikes need US spotters on the ground.