None of the new classes are especially interesting, especially considering that you have to pretty much destroy the game to get them.
Cannoneer is basically a chemist with more emphasis on direct damage and slightly better equipment. !OpenFire is kinda fun, as it causes random status effects and some minor damage to one target for free. !Combine is !mix with only damaging effects. Oh, and they get EXP Up, which gives an extra 50% EXP when equipped.
Oracle is only useful for the magic bonus and ABP Up, which gives +50% ABP when set. You also get ReadAhead, which lowers the encounter rate to negligable levels; !Predict, which casts random high level black and white spells on all allies or all enemies after a timer expires; and !Condemn, which is blue magic Doom except with -aga class spells instead of instant death.
Gladiator has 2 fairly useless physical attacks: !BladeBlitz, which does a ~1/2 damage attack to all enemies and misses frequently; and !Finisher, which misses 1/2 the time (1/4 if you master the class), does a critical hit a portion of the rest, and does 9999 of the user’s element 1/4 of the time (1/2 if you master the class). Finisher is frequently absorbed by bosses and Krile does earth damage with all the usual downsides. You also get the ability to attack from back row at full damage, but it doesn’t transfer to mime/freelancer, and to jack the encounter rate way up.
Necromancer is essentially a pumped up black mage with some minor drawbacks. Being stuck as undead and not being able to use Bone Mail is kinda meh, but at least one of the spells it gets is a double strength drain for 15 mp. The other draw back being that the spells it gets are pretty pricy: 38 mp for what amounts to a -aga black spell with a chance of a status effect to one target or 66 mp for what amounts to a Bahamut clone only with evil looking laser beams. You also get !Oath, which does ~700 damage to 1 or all enemies by calling an random crappy monster to attack.