X was an amaing game. X-2 was good, but it took me six months to play it, which is strange for a Final Fantasy game for me. Usually I play them nonstop until I beat them. I bought VIII and played it, and gave up cause I didn't understand the system. Then, about a year later, I played it again and fell in love with it. By far the best Final Fantasy.
XIII for 360 is a huge steal for Microsoft. It's not being released in Japan, though, which is a huge mistake. People would actually buy a 360 for this game, especially when the copies for PS3 sell out.