If you ever play DoT build like Firebolt sorc before, +Dot damage is the best affix. It will instantly increase the skill damage of the DoT. Just get gear with +DoT and hover your mouse over your skill’s tool tip. Check the new base damage and find the big jump of the number.
I got a 4 GA Shattered Vow, hope this change apply to existing gear. It works on all DoT build as long you can use polearm.