I don't think my party was particularly strong and we did OK, although I do have prior D&D experience. I can't remember the details, or how many attempts it took the first time through (I replayed part of act 2 and it was really easy because I knew what to expect), but as others said make sure Aylin is up and active, and don't get too close to the avatar. Even so, I usually had one or two at risk from his fear beam and proximity effects. Ah yes - Lae'zel would probably have been on the platform with him because she was built as a greatsword warrior, and Tav was probably up there using bard spells to ward off fear effects (with halfling bravery to help). Then Wyll & Shadowheart doing ranged attacks.
That fiend in the Sharran temple was much harder, and that's not even a boss fight.
