Most of the time the caster AI does just fine without any input from the player, with one major exception, they are extremely stingy with healing spells and can't cast them outside of combat. There is no need for buff spells, as you will only ever need them on extended dungeon crawls, and most of the interiors are very small, and they take too long to cast. The Mele AI, however, often seems content to just stand around and do nothing. Also very annoying for those who picked several of the two weapon fighting feats, they shift back to one weapon constantly, defeating the purpose of the feat purchases. Then there is the 'rubber banding' issue, causing the party to do anything from teleportation to moving off in the wrong direction.
Please note that none of this is unique to SoZ though.
I'd wager the most effective group would be an all caster group of two healers and two damage dealers, all with some carefully picked summoning spells to provide the meat shields.