I find Daesh far scarier than other Islamic fundamentalist movements because their techniques are more sophisticated and their aim is much higher. The "they're killing us!" argument is so silly... terror attacks are to stir western nations into violent action, not to actually significantly injure us. And it works - far too many Americans and Europeans live and act politically in abject terror of very low-impact, unlikely events.
What scares me about Daesh, though, is that I think they're trying to goad outside powers into massive wars with each other! This is why they've attacked everyone - the US, France, Russia, and all the major Arab nations. Everyone is off fighting in Syria, and not as a unified front, but a bunch of independent powers making independent alliances and jockeying for position.
During a recent presidential debate, Rand Paul wisely asked the question, "Are you ready to shoot down Russian planes?" (note: I'm not a Rand Paul supporter. I just thought he was spot-on with this.) If the US creates a no-fly zone while Russia wants to do bombing runs in it, we could have a situation where American and Russian planes are in direct combat. There's a non-zero chance that this could lead to nuclear war and the destruction of the West as we know it. And we've already had the first taste of it, with NATO member Turkey shooting down a Russian plane.
If I wanted to destroy the West, that's exactly what I'd do - provoke a war between the US and Russia with those giant Cold War nuclear arsenals.
And that makes me think Daesh is by far the most sophisticated and dangerous enemy we've seen since the Nazis.