Charm of Thorns damage is insignificant on Nightmare, being the same as the damage of the weapon.
Critical hits are the only significant source of damage on Nightmare difficulty for both ranged and melee builds (magick gets damage/time spells that also stun for down-damage). The damage returned should be based on some calculation including blocked damage and weapon damage and/or critical modifier rather than just weapon damage so that it scales for higher difficulties. Otherwise it barely damages things with higher progression.
