Final Fantasy III and Final Fantasy V are both built on the Job System. Your characters can change jobs at any time, which gives them access to a new set of weapons, spells and special abilities. As you advance through each game, more jobs become available to you and mastering their use is vital to success. While the system has reappeared in slightly different forms in Final Fantasy Tactics series, Final Fantasy X-2 and Final Fantasy XI, FFIII and FFV were the games that established specific job roles - and also defined the sort of characters and abilities we'd see in later FF installments.
Though you could choose your party in the original Final Fantasy, you were stuck with them for the entire game. Way back in 1990, Final Fantasy III introduced a radical new concept: the ability to change character skills as needed. You gained access to jobs with specific strengths as the game progressed, and these jobs could be changed anytime - as long as you had adequate Job Points for the change. Many jobs that are now series staples, such as the Knight, Summoner and Dragoon first made their debut in FFIII. With all of these jobs came class-exclusive battle commands - another Final Fantasy first. The game remains much the same in 2006.
Final Fantasy V is an evolution on FFIII's formula. Instead of needing to spend job points to change classes, characters can swap available jobs as they please, without penalty. Jobs also offered multiple unique skills, which can be learned by earning enough Ability Points in battle to raise their Job Level. Mastered skills from previously held Jobs can be carried over to other jobs, as well. It's a big improvement over FFIII's set-in-stone class abilities and allows for a huge amount of depth in both building up characters and fighting battles. FFV introduced many new classes and abilities to the FF series, as well - much loved skills like Double Magic, Coin Toss and Mimic were born here.
You'll like FFIII if...
You prefer a more straightforward Job System with no need for tiresome level-grinding
But you might dig FFV more if...
You enjoy creating, building up and customizing your characters exactly to your liking
