They kill me lots!
I've built up a reasonably useable VT5 Nightblade (my only character) and have largely managed to work around the build's limitations, to the point where I can solo some world bosses, handle largish groups of MOBS and usually work out tactics to handle any equal level enemy, but Storm Atronauts seem to cream me every time.
My usual arsenal of attacks just don't seem to work for me here; I can't stealth around them (their electrical field breaks shadow cloak), I can't stun or snare them, I think that I take constant damage whilst engaged in melee and their electrical bolts are pretty effective at range too; I don't think that bleed damage effects them either. Add to that that I'm getting hit for over 1600 damage in single attacks and I'm struggling.
They've now replaced Harvesters as my most hated foe!
I am one of The Great Mediocracy, those whose role in life is to provide the baseline by which The Few deem themselves Great.