Do damage = get barrier. (KE tree)I haven't bought the game yet, but this class seems like the most interesting to me. Why is it so powerful?
Sacrifice barrier = deal more damage. (Fire tree)
...basically, it keeps itself active as long as you keep attacking, making you nigh immortal.
That is at its core - you can spec around to make it even better. e.g. Crit = no cooldown on next spell etc