The target audience for ISIS is not the West or moderate Muslims, it is to attract more foreign fighters. Unfortunately, some Muslims and Muslim Converts are attracted by the prospect of murder, rape, pillage, etc.
The target audience is indeed the West and the so-called moderate Muslims. They are daring them to come and take them out. Air power alone will never do it. Only a ground campaign will do so and only Iraq and the West's enemies Syria and Hezbollah (supported by Iran) are engaged on the ground against ISIS.
ISIS is reading the situation very well. As long as the US and it's client states obsess about getting rid of Assad first (because Syria is allied with Iran), they know they can get away with what they're doing and reinforce their claim to a separate and independent state.
Meanwhile, despite 3000 western funded and trained 'moderate' Syrian rebels having defected last year with their weapons to Al-Qaida and ISIS, stupid US politicians are going to train another 5000, and they think they can make a difference against 30,000 (and growing) ISIS jihadists.
The US and its Arab allies have to make up their minds who they want to fight: the Shiites allied to Iran (Syria, Hezbollah), or the Sunnis (ISIS) attempting to slaughter the Shiites, including the Shiites who control the Iraqi government. They can't do both at the same time. Given that ISIS is now threatening Sunni regimes (including their original benefactors Saudi-Arabia, Qatar and UAE), the logical choice is quite clear. But logic is not something US politicians and their allies are known for.