I play on extreme:
First Line: Warrior
Second: Conjuror, Cleric, Conjuror.
1st level boss is a little bit hard, but later it's really hard to lose.
Conjurors can:
summon Wargolems to the first line,
Call Souls of dead allies
and Banish all summoned creatures (even Human's Aetherguard).
With staffs they are useful to kill Wraths, and all second line stuff.
Cleric is full time doctor (with Holy Light, Purify! and Heal All).
And warrior with Execute and developed Leadership quickly become killing machine.
 "Tentacle Wars"){kind=icon}
 "GemCraft"){kind=icon}
 "Monsters' Den: Book of Dread"){kind=icon}