I'm running Second Darkness AP using Pathfinder rules, and have been converting from 3.5 as we go. When prepping the Teeth of Araska set piece from Children of the Void (#14), it seemed like Ishana would be a good witch, rather than cleric of Calistria.
I can't say this will provide a tremendous amount of insight, since I left her at 3rd level and she's a small part of this set piece. But here's what I can offer:
I gave her a raven familiar, and the slumber and evil eye hexes. For spells, she had web, glitterdust, burning hands, chill touch, and obscuring mist. She kept her gear from the set piece, which included the wand of cure light wounds.
For those unfamiliar with the set piece, the Teeth of Araska is a statted-out pirate crew and mapped-out pirate ship. For my campaign, I sprang the encounter as they were on a ship heading to the island where most of the adventure takes place. I figure this was an EL 7 encounter against four 4th-level players.
As part of a pirate crew, Ishana probably contributed more as a witch than she would have as a cleric. She cast web into the party's ship's rigging, and glitterdusted the paladin and barbarian. The barbarian was blinded for the full three rounds, limiting her involvement until it wore off. The raven familiar tried delivering the chill touch spell, but I rolled poorly during its attempts.
When the heavily-armored fighter tried balance checks to cross the planks separating the two ships, her evil eye hex made the prospect that much more dangerous.
She met her demise when the raging barbarian finally crossed to her ship, withstood the sleep hex and a burning hands spell, and dropped her with a great axe.
My impressions:
The players didn't know they were facing a witch. (None of the players had read the playtest.) Most just rolled with it, assuming she was a wizard/cleric or wizard/druid. I don't know if that matters to the designers, but nobody reacted to her unusual class abilities (the hex powers) with shock or awe. But my group's like that.
As part of the encounter, she played her role well -- delaying the big hitters who have poor will saves. She didn't dominate the encounter, or appear especially unbalanced. Hexing the fighter to give him a -2 on his skill checks as he tried to balance his way across a plank made for a tense moment.
I'm liking the class so far, but of course, this was a limited demonstration of its abilities.