Tactics has by far the best battle system in the series. Positioning was very relevant, and so -- unlike in XII and XIII -- you were given the actual ability to control your character's positions (shocking, I know). It included a ton of variety and customization options (between generic classes, unique story characters, and monsters the options are virtually endless), and often required a lot of strategy. How many times in other FF games on your first time through did you have to retry a boss fight and drastically alter your strategy in order to win? Most players had to do so at least once in FFT (thank you, Wiegraf).