Oh I see! In that case, Dissidia 012 basically is the first Dissidia but with an extra scenario featuring the likes of Lightning, Tifa, Vaan, Laguna and Kain. You seem to have played most of the games featuring them, so you'd likely get a kick out of it if you enjoyed those characters.
It does have more content, but keep in mind 012 is still basically the first game with a new prequel scenario with those characters.