decent storyline that is beleivable enough to pull you in yet fantasy enough to make you go "OOOooooOOOoooohhhh i wished we had THAT!!!!! i totally wanna cast haste on myself at work!!!!!!! $_$ payraisepayraisepayraisepayraise "

also, good music that actually fits the storyline, timeline, events, etc.

i also the the virsitality that ff offers. you can totally customise your characters to do whatever you want (fft perfect example. im a total fangirl for fft). the custom magic, equipment, materia/junction combos, sphere grids, etc.

also, the side quests make the game series more fun cuz they add more excitement and such. i dont like it when the sidequests distract from the game itself, like 12, but to where they mostly help you get stuff to help with the battles, like breeding chocobos in 7.

character development is also key. its sad when the main char has the same mindset at the end as s/he did at the beginning. it has to be like a soap opera!!!! life changing events!!!!