The DLC is solid. You play as some of the other characters. You meet some of the FF characters. There's lots of fun optional fights and 2 VERY interesting secret endings.

That being said personally, I'd wait for it to be on sale. A large part of the actual story of the DLC is just retreading through the beats of KHIII and just makes it even more messy to setup the inevitable sequels.

It's definitely more meaty than your average DLC these days, but I don't feel it's worth the $30 price tag.