I ran thru as Level 85 mage. In Selin's room there are three mobs: two of six each and two directly ahead. You can attack each without aggroing Selin. If casters attack first, he takes a few seconds to leave his platform and run down. He will, during fight, run to green, suspended stone for healing.
Tyrith is lying inside the next area, the Halls of Theory. There are a two mobs of wyrms in this hall; they are normal 70s. You can aggro one bunch at a time. A keeper will approach to kill you; Vexalis awaits your attack on him. He will create motes of energy to attack you after you aggro him.
The scrying orb is just around the next wall. It has a short cinematic to preview, I thought, the next part during which you will kill Priestess Delrissa.
Kalecgos, of the Blue Dragonflight, will appear in his human form to your right to complete the quest, The Scryer's Scryer. He will give you the quest, Hard to Kill. Keep on going past Kalecgos to enter the Halls of Theory again and face a rather intimidating mechanical, Level 71 elite who I was able to freeze in place.
The next area has many mobs of six; the first one includes both a mage and a warlock. Mages, you can Spellsteal here. You get a nice enemy mage-dampening, purple dome that heals and refills mana. The next mob you can steal fel armor and haste. Be warned, my pet started a fight with the next mob before I was ready. Definitely need casters/distance fighters in this area.Stay inside the purple dome whenever it is stolen. It's great. (My pets keep starting fights even when on Defense.)
The Priestess Delrissa is a many-armed boss surrounded by defenders. Wipe out all the surrounding mobs first, of course. Stupid pets started the boss fight before I cleared all the mobs! Fortunately, the furthest one wasn't aggroed. Run on thru the next doorway to get to the final boss, Kael'thas and all his mobs.
Exarch Larethor shows up to complete outstanding quests. The pink orb up on the platform up the ramp will port you back to the Shattered Sun Staging Area.
This is a fun and very pretty dungeon.