You can’t understate the importance of Final Fantasy IV to the franchise as a whole. Its epic character-driven story set the stage for the more complex narratives of future entries. The active-time battle (ATB) system added an element of danger to turn-based battles as players nervously waited for a character’s bar to fill. In fact, the ATB system would be so successful that the series would use it for the next five games and some spinoffs.
While FFIV set the series up for greater success, many consider it far too brief and linear for its own good.