Divine Vengeance is undoubtedly a powerful spell, especially when playing as Dwarves. But I also liked the spell that stops the flow of mana; it costs less mana than Earth Shock, and the effect is practically the same, plus there's an additional bonus from the raw damage, and that's great!

Added after 11 minutes
I want to add that while playing through the campaign as Zehir, I maxed out my summoning magic, so the Crystal Secret dealt 800 damage – not bad, huh? I was looking around and noticed that a lot of people are arguing about which creatures are best suited for vampirism. My opinion is that Dark Stalkers and Paladins are the best. They deal increased damage when leveled up (Dark Stalkers reduce the target's armor), but in the end, they kill a lot of people.