My biggest problem with all shadow priest groups? Having to switch out of shadowform constantly when doing anything really challenging. Instances at level once you hit BC are either a fear-bomb clusterfuck or hoping they kill off the mobs before dying horribly. I hated the instancing abilities of the group. They were awesome in world PVP and certain encounters due to WoTF + fear ward + massive renews/heals. My main gripe was having to pick between healing and DPS when they started getting beaten on.