Don't get me wrong, ISIS is a terrible group, one of the worst in terms of human rights on the planet. But for all their recruitment success, my impression is that they are mostly stealing recruits from Al Qaeda affiliated groups. While the various Al Qaeda franchises prioritize attacks against the West (the so-called "far enemy"), ISIS is spending most of its efforts to hold and expand their territory in Syria and Iraq. So if I view the conflict from a completely U.S.-centric viewpoint, ISIS's recruitment success is not necessarily a bad thing.
Actually, I don't think that a purely U.S.-centric viewpoint is how foreign policy questions should be viewed. But I do find it interesting when people who do view foreign affairs through that lens freak out about ISIS.