FFIII and FFV have common roots in the Job System, but they differ significantly in their combat. While FFV's battles use the fast-paced Active Time Battle system, FFIII's combat is strictly turn-based. You enter commands for all four characters are at once and the speed of the party members and the enemies determine the order in which actions resolve. Helpful markers appear to remind the player which character is assigned to attack which foe when entering commands.
The magic system in Final Fantasy III is also drastically different from what we've become used to. Rather than using a pool of magic points, FFIII arranges black, white and summon magic into tiers. Characters are allowed to cast a set amount of spells from each tier based on their level and their current job. While the GBA's Final Fantasy I & II: Dawn of Souls got rid of this, FFIII DS is faithful to the original game, due to the availability of spells being a key factor in deciding which jobs to use.
You'll like FFIII if...
You like to take your time in planning battle strategy, rather than making snap decisions
But you might dig FFV more if...
You enjoy fast-paced combat and prefer a more intuitive magic system
