Well it does have a bit of a environmental message to it with the amplifiers, yes a great evil is trying to break the crystals but Cid's machine's and people's greed are just making things easier for him. Also ExDeath's origins can be an interesting parallel to removing nuclear waste if you think about it.

Trainer is a class that can capture weakened monsters and then use them later for one time summons. When the job gets leveled up, it learns the Control/Manipulate ability which is excellent for teaching Blue Mages their skills.

Time Mage is probably one of the best new mage classes in this game and if you've played FFTactics, you know what to expect. Also don't underestimate the Return spell. It seems useless at first but it's highly invaluable against certain attacks.

Sorcerer is called Mystic Knight in the Advanced version and is one of the coolest warrior classes. They cast elemental spells on their weapons to make them more powerful and exploit weaknesses. They are more frail than Knights or Samurai but have excellent damage potential. Even better is that the spells they use is based on what White/Black magic you've bought up until now.

Ninja is pretty cool but isn't quite the dominating force it was in other installments. A huge upgrade from Edge in FFIV but nowhere near as bulltrout as Shadow, FFIII Ninja or anything from the Ivalice entries.