What exactly is Islam is difficult to define even for those who consider themselves Muslims so how even less able for non Muslims. So even if not perfect it’s best to allow Muslims to answer the question and as the vast majority of professed Muslims say they are not we should accept they are not.
Im not Islam but I'm sure there is nothing in the Koran that says put a machine gun in the back of your Toyota pickup and shoot up a bunch of innocent people. I think ISIS uses people who suffer from shear stupidity to do all their dirty work. ISIS is not Islamic, they don't care about anything in the Koran, all they want is power over others.