I've been playing Dissidia for a while, and I'm really impressed with it. There's a lot more depth to the game than I had imagined there would be. It does have one major downfall: the story tying all the characters together is absolutely dreadful. I can't take it seriously, but I need to play through it if I want to get any of the good stuff. There is arcade mode, but all the characters are locked to a specific set of abilities and equipment in it. I wonder if hard mode arcade is any different, but I haven't bothered to unlock it yet. Other than the story, though, the game is top-notch. It has decent voice-acting (aside from repetitive in-game clips like shouting attack names and so on), great graphics, what seems to be great music (though I can't really tell since my headphones have died), and even its own "achievements" system.
Thus far I've completed Cecil, Cloud, Squall, Zidane, and Tidus' stories, and I've started on Firion's. I'm not particularly enjoying it because Firion starts with a single slow-moving projectile HP attack for both ground and aerial movesets, which makes it a pain in the ass to actually finish any battles. One might think he would start with more, being a "weapons master", but one would be mistaken. Oh well. My favorite character might be Cecil, but I haven't tried them all just yet.
I almost forgot to mention, after a certain point in story mode you unlock the ability to save battle replays. I haven't looked at this in detail, but you can also use this functionality to save battles to motion jpeg and view them in the XMB or, presumably, copy to your hard drive and upload to Youtube and what have you.
