Unless you already know the main characters making up the various Chicago mobs of the 1920's and 30's you will most likely not understand this movie. It is mostly a collection of well-known incidents (the St. Valentines Day Massacre for example) and extreme violence along with standard "mobster meets dance joint showgirl" interludes.
Because the entire story of the Chicago mobs are not explored in greater detail and the actors don't look much like their real life counterparts it is often difficult to follow the action when one gang is attempting to waylay the other(s). Even the 1950's TV program "The Untouchables" offered a lead-in before each episode that explained a bit about the history. This movie just begins cold.
I gave the movie a 3 for the photography, sets and costumes but the storytelling leaves a lot to be desired. Anyone who knows the actual history of gangs in Chicago will wonder why they made this movie.