There are many systems layered on top of each other and combining them into successful strategies can be immensely satisfying.

For example, I once attacked a large army with a single Vampire Lord. The game warned me against it with a prediction of "certain defeat", but because I had specifically built that Vampire Lord around large mana regeneration, he was able to take down the entire army by repeatedly summoning shadow horses to charge at them while teleporting just out of their reach. Good times.