Final Fantasy proper gameplay have always been a mix bag, from somewhat basic to a borderline chore. But it was always varied. (IMO), the most original and consistent thing Square put together on that front is the job system. For philistines, it's a class system in which you can mix and match classes. Typically, you master class A to the point you learn a permanent skill that you can use in class B. A straightfoward example would be to level ''NINJA'' to learn dual yield and use it as a ''KNIGHT'' with two Cloud-grade huge swords….
Which lead to what, (IMO) is the weakness : it's a system that offer a huge freedom on purpose and did break on occasion from class models (example : FFT made healing with pots viable with the CHEMIST), but it was never researched, since some combos were gamebreakers even by JRPGs standards.