Warlock's primarily use Hellfire Ring against mobs to apply a curse on the enemy.
Quite a few enemies can see and engage the player within the Hellfire Ring cast range. These enemies can also close the distance quickly towards the player resulting in Hellfire Ring being cast at the location where the mob used to be and hitting no enemies.
To combat this issue, I'd suggest a change to Hellfire Ring's casting by one or more of the following:
* Reduce the cast time
* Increase the cast radius
* Bring forward the actual time within the cast process when the Hellfire Ring actually appears and applies the curse.
This would make the power a little more player friendly.