Really, I have beaten Oath and am at the final boss in this game and I've got to say that these are some of my favorite bosses in any game ever. The sheer amount of attacks in even the early bosses (comparitavely to other games) is very impressive, to me. The fact that these bosses manage to be pretty much skill based (except maybe Khornscarld which requires having a certain amount of damage to beat unless it has an anti stalling mechanic like Pictimos and loses the ability to heal eventually) in an RPG removed a lot of the doubts I previously had about these games before playing them, and aside from that boss I've never had to do any grinding at all.
So, basically, the bosses in this game just rock IMO. Definitly as far away from the "damage sponge" archetype as you can get.