Although Crying Freeman is not at par with Kazuo Koike's obra maestra The Lone Wolf and Cub (god that series is just amazing), I throughly enjoyed reading this as a guilty pleasure material. 
 Crying Freeman's protagonist is Yo Hinomura, a talented, kind and morally untarnished man who got into a series of unfortunate encounters with The 108 Dragons; and with acupuncture and training from really old people, he ultimately became the mafia's top assassin. But after each kill, he is filled with guilt and remorse, something that makes him cry, hence Crying Freeman. 
 I said it is a guilty pleasure read. The material is filled with violence, sex and murder. The plot is what you expect from a mafia-assassin genre: kill contracts, love interest, training, murder and guns. Ryoichi Ikegami perfectly captures all these in his art style which is so detailed and alive. His drawings of cars, buildings and inanimate objects are exact and his characters are full of emotions. 
 If you are looking for an adult manga about modern mafia and assassinations then look no more. Here's Crying Freeman.