Frost basically became the #1 raid viable spec now, with an interesting rotation and a pet you don't have to glyph to get permanently and it can still Freeze, which also interacts with your rotation. This is shit they could have solved two years ago but nooooooo.
Fire became the AoE spec that is all about lighting shit on fire. 10% haste when three or more targets have your DoTs on them means they will need to either balance boss fights around it always being up or never being up and it does have some interesting implications for PvP. Nevertheless, looks to have similar gameplay as before. The new HS is weirdly split into two different talents for no apparent reason but the new Combustion, Blast Wave and Flame Strike are all rather interesting, at least at a glance.
Arcane is the big problem here. Arcane was always about burning mana to get extra damage. That still applies, AB only synergizes with itself now and AM is a proc but that is practically how it was before too. But the mastery gives extra damage the more mana is in your pool, which completely counteracts the whole idea of having intense burn phases heavy on going through the mana pool in record time. Instead, the most beneficial way to play should be to use a conservative cycle that will let you mana gem back up to 100% and then start a burn cycle that will last until you evocate back up to 100% again and then start the conservative cycle again. 98% extra damage for 700% extra mana at 4xAB is just by no means fun and the burn cycles are super slow and not that spectacular, which was some of the arcane allure. The absolutely worst bit about the entire thing is that the rotation is going to be pretty much exactly what it always was.
About the new spells, the frost one is underwhelming and heavily situational/PvP oriented, the fire one is just another mindless thing you shoot on cooldown for Fire and Frost but ignore as Arcane, and the arcane one is, hold on to your seats if you managed to miss all pre-Cata spoilers: Mage Bloodlust. Yeah. It's an exact clone of Bloodlust so that your ten man raiding team (which will probably start being a rather big part of raiding with the new changes) can get by without a shammy. It also gives the mage some extra soloing/PvP oomph which is nice I guess, but fact of the matter remains, they copypastad a very uniquely shammylicious spell that has been part of their lore since Warcraft 2 (although the unit casting it then was called Ogre Magi...) onto mages just for the sake of balance - the lore justifications are weak at best.