Most maps i've played that include them just either put them at the bottom of damaging pits, in really dark places or heck, both scenarios at once, it's really annoying trying to run around dodging attacks only to bump into seemingly nothing and get a chomp right to the face.
I don't find them to be the hardest enemies, i don't even find them the most annoying enemies (Pain elementals and Revenants take that spot), but i just find them to be a really sucky addition to Doom.