Every ability is more powerfull. Shorter enrage timer and double the hit points. (but not the mana)
The hard part is in dealing with the exploding shades.
You can have classes that are better suited for single target dps such as rogues full time on the shield.
Classes that have both magical and physical damage (ele shamy, retri) can also choose to stay on the shield if adds die fast enough.
Adds will keep spawning in phase 2, but only from one side at a time.
Immune to taunt.