The primary themes of the film involve trust and betrayal.  The movie was really quite good in bringing a new angle to this depiction.  The idea of the outsider attempting to infiltrate the inner circles of the mafia family had been shown quite a bit.  The film depicted a new depth to this old tune though in developing the relationship between Joe/ Donnie and Lefty.  The disillusioned veteran assisting and taking on the rookie acquires great meaning in both the film and the idea of Pacino working with Depp.  There is an emotional connection that both forge, a depth that almost belies the instant betrayal that will happen.  Another theme of the mob organization as being a lumbering giant in the 1970s is also explored in the film.  Both of these themes are explored well in the film, which someone could not say "fuggedaboutit."  (Sorry- Had to put that one in.)