Alright so I played a little bit of Dissidia 2009 when it came out and it never really clicked with me, granted I didn't give it much of a chance.  
 I have a couple questions about this one: 
 
1. world map?? I heard the chess-like advancement grid has been replaced with an overworld? This alone might be enough to reel me in! 
 
2. Is it true that the entire Dissida 2009 is unlocked after you finish the game? In other words, probably no point playing Dissidia 2009 first right?  

@bigmuffpi: 
 
1. There's a world map but the majority (if not all) of the story battles consist of gates on the map which lead to the grid you know and love. Whether on the world map or a grid, you're pretty much collecting stuff and fighting other dudes anyway so that shouldn't be a deal breaker.
 
2. From Gamefaqs: 

Original Dissidia Story

Beat the game and you will get an option in the story selection which is the original dissidia story 
 
Thank goodness I got to try this out before buying because I was under the impression that Duodecim was going to be a proper 3d fighting game and not a RPG/Fighter mishmash. I couldn't play "Action mode" to save my life and had to resort to "RPG mode" for combat because the damn camera and playing fast paced fighters in big stages don't work on a small low-res portable.

If you're looking for a FF fanwank, this game has it in spades but if you're looking for a good RPG or Fighting game system, this thing fails hard.

The Game has a LOT of content and its really fun , I just recently finish the 012 storyline and a whole lot of options open up the Story of the first Dissidia  its one of them and the bes its that it plays in the style of the Duodecim strory so yes the world map and the Grid gate dungeons, wich if you played the orginal those are very much improoved and much easier to understand the whole gain more points by chaning groups of enemies , its a lot more fast paced than before thats for sure and this of course makes the first Dissidia obsolete if you want to play go buy Duodecim , and about  the game I wasn´t even that big of a fan of FF to be honest but when I got into the first game I had a blast and in the process I learn a lot of Final Fantasy story, if you´re a fan this is a love letter for you don´t missed out its really fun