[PS2] Kingdom Hearts 2

I just got this game last thursday and I've been having a great time with it. I won't repeat what's already been said but I just got to

Spoiler:

Hollow Bastion where the darkness is covering it and the big LotR style war of heartless is happening

I think that the Sephiroth/Cloud thing is just a bit over played myself but as long as it doesn't become more important than rest of the story it'll be alright. The gummi ship parts are a lot more fun now, almost Star Fox fun but I'm to lazy to build my own gummi ship so I just stick with the pre-made blueprints.

I have a question though, I haven't completed Atlantica yet and I read some where that I should complete the worlds before going back to Hollow Bastion. Do I really need to?

Jam it back in, in the dark.