Well...the characters are portrayed in a VERY stereotypical way. In that regard, the show is not very different from all the bad mafia/gangster movies we´ve seen before.
Lucky Luciano, for example, is portrayed as an volitile, restless knucklehead. And Torrio is just a simple pimp and a smalltime bootlegger according to the writers and producers of the show.
What I think would be great is a show where the producers actually spend some time in serious researching regarding the characters before putting together a show like this. But not only researching the characters, but also good, solid researching in events that we consider as mafia/gangster historical milestones.

I am aware that Boardwalk Empire does not pretend to be an historical
documentary, it is a work of fiction very loosely based in
part on some historical figures. But as such, I´m sorry to say it, on the cost of authenticity.
Don´t get me wrong though, I enjoy the show.