World of Warcraft Class Q&A Series: The Warlock

Blizzard continues their World of Warcraft class Q&A series, and this time class design team member "Ghostcrawler" answers questions about the Warlock.
Community Team: What is it that makes them unique compared to all other classes?

Ghostcrawler: Demons are a big one. Warlocks are a pet class, but they gain more of their own power from their pets and can make their pets do more than say a hunter or death knight. The way they do damage is different from a mage because a lot of their damage, even for Destruction, comes from damage-over-time spells instead. Warlocks bring some utility that doesn't strictly increase raid damage, so we feel like it's fine to keep those abilities unique to the lock -- things like summoning and health stones. But again, we think the real way to keep warlocks from feeling like mages with pets is to do more with the Soul Shard mechanic.