12's battle system was excellent imo, based roughly off an MMORPG (FFXI) battle system while still retaining loads of elements of traditional FF games in the past, it was a truely unique battle system for this game, as far as storywise, the game's monster hunting led me way off track of the story and when i returned to beat the game, i had totally forgotten what the story was about.
13's battle system was also great incorporating paradigms which required strategy but i noticed it carries over what they did in 12, which is you are only in control of one character while the other 2 characters play off preset commands....i hope that if they ever do come out with a final fantasy 15 that isn't online based, it will allow the traditional rpg battle system where you are in control of all 3 or 4 characters