Take a look at the official and un-official notes for a comprehensive look at what will change. Nothing in the patch is game-breaking, in my opinion, but there are some nice changes. Some of the major highlights include:
- Changes to the way arena points are calculated.
- Void Shatter no longer has a cooldown, and other cooldowns have been reduced.
- If you are sheeped / polymorphed by a mob, you will no longer gain back health (ie: the mass sheep in Aran, which regens your health before he fire blasts the raid).
- Many main hand weapons are now one hand weapons.
Edit 3:24 p.m. EDT: It should be noted that the final version of the patch notes have not been released yet, however they are usually close to what the PTR patch notes are.