It really isn't. I started doing some personal tests as soon as it happened. Fire feels awkward with the reduced crit, and performs poorly. This isn't coming from some random terrible mage, I've been a well ranking fire mage for a long time now.
http://www.wow-heroes.com/character/us/Arthas/Shmek/
Our guild transferred this raid week, so these are the only ranks showing on wow-heroes.
I highly doubt it will be strong compared to other single target specs. Frost and arcane are superior, though arcane is barely functional in a raid environment.