COM:
Role bonus is much lower, about half of what it was in FFXIII.
They have a ton of new auto-abilities that raise damage; most of these don't stack with each other though.
Powerchain appears to have been buffed.
RAV:
Other than the new skills, they appear to work the same.
SAB:
Role bonus starts very low; at Bonus Boost II it's a bit lower than it was in XIII.
I don't have any info about accuracy for the spells themselves at this time, unfortunately.
Wound and Woundga
All skills inflict Wound damage.
The normal spells received a slight damage boost.
Curse makes a target take 33% more Wound damage and lowers Keep.
Deprotect and Deshell are a smaller bonus.
Dispel attempts to remove 2 buffs per cast.
Endless Nightmare (damaging move that slightly boosts debuff duration)
II/Heavy skills are physical, with higher attack multiplier, cut and keep.
No Daze or Slow outside of Feral Links.
SYN:
Role bonus is much lower.
Most buffs seem to have longer base duration, perhaps to compensate.
-Ga buffs are cast on the whole party, but wear off very fast.
Brave and Faith are basically equal to Bravera and Faithra in the previous game: big boost with a short duration
Vigilance is now Wound damage -33%, Keep+20; There is no way to raise Cut in this game outside of the "Pressure" passive
Endless Blessings adds ~8 seconds to buff duration.
No one learns Barspells or Haste.
Enaero replaced Enwater.
MED:
Role bonus is lower.
I'm not sure how much is Raise itself vs. Improved Raise II, but characters revive with more HP. Max seems to be 50% (in FFXIII Lightning with Improved Raise II capped at 36%)
SEN:
Role bonus is more front-loaded, and doesn't protect allies quite as much. (9% vs 15% in FFXIII)
Role Bonus has a Wound Damage lowering effect.
Lost all evasion related abilities: Evade, Counter, Elude
Steelguard increases resistance by 5% per hit. (1-2% in XIII)
Element Guard lowers elemental damage for the whole party by 33%.
Can't say for certain here, but it appears Entrench's bonus may be higher (My Metalligantaur is doing quite a bit more damage than it "should")