Let me break down how great this spell is:
Check out the resist adjust. -1000! I've had it resist about a total of 3 times in a week of play.
You might have missed the cast time, it's 0.75 seconds.
It also has a low mana cost, only 273 base mana.
The only downside to this spell is the small 4 second recast time; it's nice, quick, reliable damage. This spell also procs the radiant mana AA's frequently too, so if I find myself low on mana, I will chain cast this until I get a radiant mana proc and follow up with a big nuke and repeat until I get a chance to recover. Damage wise, it does at least 1800-2500 normally, occasional 4000+. Crits are anywhere from 2500 to 8800. Count on this doing about 3-6% (non-crit) of a mobs health around the level that you get this.
It's a great finisher or pulling spell. Highly recommended!