Having played through all of the dungeons now, well, you get to rescue tonberries. That alone makes the last set of dungeons worthy.
As in every set of dungeons, there are winners and losers amidst the bosses, good points and bad ones. The dungeons as a whole are very reluctant to let you do much speeding through, with pulls being pretty aggressively gated. So let's talk mechanics, let's talk atmosphere, and let's carefully coach you through the process of kicking the crap out of your final expert roulette competitors.