While you won’t play as Niko Bellic he will make some cameo appearances throughout the add-on. Dan Houser, said that he didn’t want to give the plot away but that Johnny is a very different person and character than Niko and that players will see Liberty City in a very different light.
Meanwhile the screenshots remind me a lot of the FX show Sons of Anarchy (I just watched the last episode which was great by the way) and this can certainly allow for some lovely language and action scenes.
Sam Houser also mentioned that there will be two episodes and that “We hope fans of the game enjoy the new way of experiencing life in Liberty City contained in this first episode.”
So far no price has been given but it’ll be interesting to compare sales of the add-on to those of Street Fighter IV which comes out the same day.