Yeah well I've played a warlock since 2004 so there.
It does about as much damage as a Chaos Bolt, for cheap, at a decent frequency. Balance is just starting, so we'll have to see where it falls in the end.
Actually, the legendary gives fire spells a chance to generate a shard, which is every spell Destruction can cast except for Shadowburn. Chaos Bolt is chaos damage(ish) now, remember, and that includes fire.