ONE: You regain health by executing enemies. Not, in an of itself a problem, BUT... you are not safe while executing enemies. IE: You continue to take any damage while locked in what is typically a five second animation.
TWO: Horde battles with very little in the line of incentivizing you for doing it, while at the same time having objectives that you need to carry out during said battles. There is very little one on one combat, and even less of it is provided with a reward attached.