Really, some of the graphics are crap, and some are Playstation 2 graphics and better. Just most of the scenes you see online are the times when the graphics are bad. It varies.
I'm going to tell the storyline in the beginning so if you don't want to find out yet, don't read on from this point. *Spoiler Alert*
It starts out with Roxas in front of the castle thing Sora is locked in KH2. Then a guy (who I think is Axel) comes up and asks Roxas if he wants a purpose in life and then he joins the organization. Roxas is "zombie like" for the first few days, but then he meets Xion who is also basically a zombie. Then after a few missions, Xion opens up, takes off her hood and officially becomes friends with Roxas. I also forgot to mention that every day after a mission, Axel meets up with Roxas and later Xion at a clock tower where they have sea salt ice cream. This is sorta minor at the beginning, but I think it grows more important further through the game. If you want me to tell more, please let me know. I just wanted to tell what the start is like.
But seriously, get it! It may look crudy, but if you liked the other ones you'll love this one. But I highly suggest playing KH1 at least, and recommend playing KH2 before playing the game or you'll be confused in points.