He is great against all the different "brutes" that evil players can use, call winds can keep a troll away from your frontlines for up to two turns and natures wrath is always useful. I have used him twice, in one game i was defending a fort, i placed him right behin the gate and cast natures wrath, it really paid off and got 4/5 half trolls killed
In the other game he wasn't as much use
he did stop a chieftan getting into my frontline but only managed to cast natures wrath once. In both instances i was using him as an ally for dwarves and i'd say he did pay off, if i were making an elven army and had to choose between him and a captain, i would choose him. Im actually thinking of bringing one to the GT in the rare occasion i come up against a troll or similair monster