I think it'd be about as action-filling as most other fights in BBS to play... and by action-filling, I mean somewhat annoying. I'm used to seeing the annoying enemy of all the enemies in games... but BBS... it just seemed to have a lot of that kind. Or maybe it's just me.
Also... I almost want to say you get to face Darkside but... if I recall correctly, Darkside has yellow eyes, not red. That, and I think he'd be too easy a boss for any Secret Episode.
Then when some guy beats him on the first day the game is released, they'll try and make a new secret boss for the next KH game (most likely to have a secret boss) and try to make that boss EVEN harder.
I said that. I'm saying that he can only steal Soul Eater cards because of something in his or the cards' codes or both. It may be why Zexion doesn't steal and use Keyblade cards and treat them as Soul Eater cards.
I would say that it's because he eventually uses the stolen Soul Eater cards and can't use Keyblade cards or treat them as Soul Eater cards. And there's normally no reason to try to steal other cards since, as Riku, you would only really have Mickey or Item cards besides your attack cards.
There's probably something in the cards' codes that prevents Zexion from treating Keyblade cards as Soul Eater cards.
If I didn't know better, I'd say that the Terra vs. Braig battle is going to be very similar to fighting Xigbar in KH2(FM) based on the two screens of that boss battle. It looks like it could be unless I'm mistaken.