I would HIGHLY recommend you to take Shadow Walker in Nerekhall (not especially with Tinashi by the way) !
It's a lot of fun when you see that many of the quests are determined with a search action who is often far away or behind obstacle. With a Shadow Walker, you can take them from far and still be with your mates, then go away right to the next quest's objective and win the encounter easily.
We reversed lots of quest in our campaign only with this class, who's nearly cheated in Nerekhall to my mind
(Obivously, the Treasure Hunter is even better, but this class is out of consideration since you don't even need to be good and to win quests in order to stuff your team and **** the Overlord...)