ISIS is very Islamic, the religion preached by its followers derives from learned interpretations of Islam and all their actions are based on it.
They label them selves as following “the Prophetic methodology”, following the prophecy and example of Muhammad that is taught in the holy books of Islam which is very very violent.
They also believe the end of the world is near, and are under going actions that deems them 'worthy' for Mahdi ( Mahdi is the prophesied redeemer of Islam who will rule for five, seven, nine, or nineteen years before the Day of Judgement and will rid the world of evil).
They are following literal teachings of Islam, which has many many versus about killing non-believers which is also represented in the brutality of Middle-East early age civilizations.
The Islamic religion is a serious problem, many Muslims are aware of this, no need for non-Muslim people on an online forum to get offended and defend something most Muslims willingly accept.
There's even a person from Saudi Arabia on this forum that has openly talked about how horrible the Islamic religion is especially in Arabic based countries, yet some people are still here trying to defend the religion.