I like the way they did the magic system for than regular MP (Was it like this too in the old FF3?) and I like the fact shops give you discount for bulk shopping.
I'm not sure how the DS version does it, but I presume it's the same as in the original. Namely, there are certain "levels" of magic, and every level has a certain amount of MP. So while you might be able to cast a low-level magic like Fire 7 times, you might only be able to cast Fire2 3 times. Bulk shopping was in the original too.
The class system really doesn't ever reward you for doing anything than making your entire party a bunch of Black Belts and never changing them so you are punished for exploring the game's primary feature.
It wasn't like this in the original. True, using Monks did mean you'd get an extra HP boost after every level-up, but it's not really recommended to use a party of four Monks, especially at the beginning of the game. It's
possible, though. But not very easy.