These talents, I'd consider mandatory:
* Divine Purpose
* Light's Hammer
I'd also recommend taking these:
* Long Arm of the Law
* Selfless Healer
* Unbreakable Spirit
Also -- and I can't possibly stress the following enough -- make sure you are running Glyph of Mass Exorcism and Glyph of Divine Storm. If you're running Glyph of Divine Storm along with Divine Purpose, you'll get a 5% self heal every time DP procs, and you will need it.
Avoiding the damage cone wasn't hard at all -- just commit to getting way behind him when he casts it and stop DPS during that time. Put him to sleep with Repentance often (right after he casts the bloods), throw down a Light's Hammer in the middle of them, and Mass Exo/HoTR/Divine Storm the crap out of them. Then self heal (you should have a free Selfless Healer proc by then) and you still have time to move behind him and get a free shot at his back while he's asleep (damage buff in that position). I got off several crits of close to 1 million while "waking him up."
When he casts the mirror images, Judgement one of them. With Long Arm, you'll speed through the rest, dropping HoTRs, Divine Storms and Mass Exos.
On all of my wipes, it was because I screwed up the Repentance cast. Took me 33 minutes to get the cloak.