ISIS is much better organized, and seems to have an intelligent leadership unlike their predecessors (the Al Qaeda). Al Qaeda made the mistake of attacking the super-powers, even before it had firmly established itself (talking about the 9/11 or the September 11 attacks). ISIS is much more careful. So far, they have refrained from attacking the US, Israel, and Turkey.
Which is precisely the reason why the US doing little or nothing to stop them right now is a BAD idea. They are a different type of religious inspired psycho, the likes of which the world has not seen in a long time. Action needs to be taken, and this time, it is going to take a lot more effort to get rid of them because they have grown far too strong.