I forgot to mention that, although I've played FF7, FF10, FF12, FF Tactics, FF11, and FF7 CC, Crisis Core was by far my most favourite.
It's the only one of them all that I absolutely could not put down. I really felt like we got a healthy display of Zack's development from the new guy who whines a lot, to the respectable, self-sacrificing hero he finally earned the right to be.
Add on to that beautiful cutscenes, enjoyable combat (albeit a few too many random encounters when you LEAST wanted them), and plenty of solid supporting cast, and it became a respectable addition to the FF universe. (Obviously, this is all my opinion.)