Especially with call the dead and darkstorm, darkstorm to heal, and call the dead is absolutely fantastic, especially when you are playing free for all in the story mode with two or more enemies. Just walk up to the corpses and you have half an army.

Until you get face to face with someone that does crushing damage ... or your hero gets sniped or assassinated.
The Undead race is pretty powerful but very vulnerable in early game , in addition all spellcaster heroes are pretty feeble at early levels.