I think battlefield-wide spells are really cool, particularly ones that do good things for you and bad things to your opponent at the same time. That said, Realm of Chaos did far more damage to my army than it did my opponent when it decided to put Blazing Martyr on my hero and my favorite squad of heavily enchanted crossbowmen. For 140 mana, the thing ought to come with a warning label, or just NOT occasionally suicide my own fighters.