I saw a trailer for this game when watching the GTTV Skyrim footage and I was completely puzzled.
What does it have to do with Assassin's Creed?
Is this essentially a fighting game series, like Street Fighter, but with characters from other games?
Well they have had character tie ins for a very long time.
Yoshimitsu was borrowed from the tekken series for instance.
And each game has been a different version of fighting games, all with generally the same vs though.
SC on DreamCast had an entire mission map with little stories. I didn't play II, heard III was great with some awesome characterization elements that carried into IV, and IV again dropped the mini-missions in leu of the Tower missions and story mode.
As Dovahkinn said, they have their own cast.