Short on time, so i'll cut long explanations, and just say:
*Get Rime
*Get Icy Reach
*Get Chill of the Grave
*Get Howling Blast (If you're going that far in the tree already and not picking up a 21pter)
*Consider picking up Toughness
*Consider dropping Imp Icy Talents
*Consider dropping Necrosis
Otherwise the build sees fine if you're going to be running with a healer. If you're going double DPS or light healing, a blood sub would likely be more beneficial.