I'm not even remotely here for Kingdom Hearts, but Final Fantasy is my favourite game series of all-time.
VII, IX, X and XIII >
I just finished Crisis Core for the first time not too long ago. even though you go into it knowing exactly what'll happen, nothing can prepare a person for the ending.
Final Fantasy XII is an underrated gem, being the last one on the PS2 and coming after the online one. It started off slow, but became super addictive in no longer than an hour or so.