Armour 'dancing' is off. You choose one shield and that's that. Most frost mages will probably only run Mage Armour shield which gives a base 5 mastery off the bat, as frost shield doesn't give physical resistance. What does this mean? Mages will be the epitome of glass cannons. They lose a tonne of survivability and I can see us being trained to death.
Mages only have 2 novas now (3 if include frostjaw). Cone of Cold no longer has a root. This nerfs the control mages had by a lot. 1 frost nova every 25 seconds, good luck peeling melee. The control we had in WotLK was far too much, but just right in Cata with the DR's.
Deep freeze just being a stun, and no longer adding the freezing component. This bit's annoying. Every class (except priests) has an interrupt on a lowish cd. Casting frostbolts will be impossible with a shammy hounding you with interrupts on top of a rogue kicking you. Yes, you can cc them enough to start chain casting but what then? 20% chance to gain FoF, the only time you'll be able to do decent amount of damage. If Pet Nova gives 2 stacks of fingers of frost then this is alright.
Icy veins lasting 20 seconds, but 3 min CD. I'm not a fan of this, purely because at the moment purge remains unchanged. Hopefully they change purge and bring it in line with all other offensive dispels (and also change spellsteal).
Though we will be incredibly squishy, we will have 2 shields (ice barrier and probably incanters shield). I would pick incanters shield because mages will probably be the kill target, and when you pop that you can counter pressure with 30% spell damage instead of having to sit on your rune or get a 6 second evo off.
Casting, the fact that blizzard is encouraging casting instead of ice lance spam means we'll be seeing a lot of these kids who rerolled mages quitting because they can't play them well any more. They will become a more difficult class to master, but still incredibly simple at the core. (spam frostbolts)
Frost bomb: a cool spell, but personally the cast time isn't needed. They only time you would use this is when your team is completely in control of the match.
What needs to happen in order for mages to be good
Currently, mages will probably be where they stood in wrath. Good in certain comps however not that great overall with little synergy with most classes. Their cc has been improved with regards to polymorphs however personally I feel their peeling ability has been hindered (CoC for example) If mages are to be good, haste needs to be found in gear. Most of our spells currently have cast times (frostjaw, poly, frostbolt) so in order to do damage haste is a must. However if you cannot get a good amount of haste, mages will be what they were in cata, except with less damage, less pressure and less burst which is not good.
Feel free to post your opinions and correct me where I'm wrong, I'm relatively tired