This ability is amazing.
I had a quest to kill 25 ogre warriors and mages in Nagrand. The warriors are easy. The mages die more easily, but they put out a lot of hurt. The frost bolts are easy to interrupt, but that seems to trigger a fire blast which can take out 1k+ health. For a class that can't heal, that sucks. But it can be easily turned against them. Since it follows interrupted frost bolts, I can simply interrupt the frost bolt and then throw up spell reflect for an easy 1000 damage and saving myself the lost health.
For tanking it combines well with shield bash. I pull two casters, interrupt one so I can drag it back, the other I will still have to LoS. But while doing that it might still get off a cast, I can bounce it right back. This has been very useful in Auchenai Crypts where the soulpriests put out 1k shadow bolts.
I got lazy and just copied this from my forum post a couple weeks ago.
Interrupting just sounds so unlike a paladin. It sounds crude. Shield bash? Why do we need to hit people with our shields? The Light is our weapon. Let us instead put all things to good use.
mana cost: ?
Castable on friendly or enemy targets
If cast on a friendly target, the next enemy healing spell will be redirected to this target. Imagine bursting someone down and a shaman goes to NS-heal, only to end up healing your ally.
If cast on an enemy target, the next enemy spell will be redirected to this target. Think spell reflect, but more flexible.
Let our enemies do all their evil deeds, we will turn them to our advantage.