I made a vengeance paladin playthrough to lvl 70 in hell, then abandoned it.
Actually its single damage is pretty nice even with crap weapon. But only because of Conviction pairing. Without conviction the damage is very low. With Conviction its like Tripled!
I kinda enjoyed smacking monsters one by one. But i find the big Cold length on vengeance useless for single monster affected. Therefore my AoE idea.
Btw. in recent d2R patches they made single attacks less interruptible, so its much better. Some kind of FHR or interuption immunity for brief period of time or something. Works well for Vengeance style.
Well I still think AoE hit in lets say 3 yards every 3rd hit will be very nice addition.
If that doesnt suit most of players, then let Vengeance elemental damage Deadly strike! (I would advice the same for Sacrifice skill (self harm dmg remain without deadly strike) ) And increase its %ar to 15% per level. Its enough. Conviction is enough for high chance to hit.