If a crime/gangster film is a borefest for you, try "Analyze This" with Robert Deniro and Billy Crystal. It's a pretty good comedy about a gangster falling apart and seeking a therapist's help.

City of God is pretty good movie too about a kid trapped in a city of crime.

Lock, Stock and 2 smoking barrels is another good movie to get a hold of.

Movies about gangsters/crime usually revolves about "honor" or "code" and are usually tested against that tradition of "Honor among thieves". Movies like "Young & Dangerous" usually talks about loyalty in most of their films. In Goodfellas, Henry (Liotta) grew up admiring the Mafias because they represent what society lacked, a close knit family that doesn't betray each other, look out for each other and the prestige of being famous, a close resemblance to celebrities. The situation became more dire as Henry Hill cannot trust anyone in his mob family and fears both for his life and his family's lives as Jimmy (Deniro), whom Henry admires when he was a kid and treats Jimmy like an older brother, starts whacking off everyone who got involve in the heist, because Jimmy refuses to go to jail if caught.

Gangster/crime movies presents us as the neccessary evil archtypes to counter the world that revolves on black and white. In their actions, most normal folks would consider taboo but are facinated by their concept of "life" and how they live their "lives". What we, the normal folks, normally couldn't or wouldn't do, they do it without hesistations. Another good example in Sword Fish when Gabriel Shear has a conversation to Stanley in the bus.

Stanley: How can you justify all this?
Gabriel: You're not looking at the big picture Stan. Here's a scenario. You have the power to cure all the world's diseases but the price for this is that you must kill a single innocent child, could you kill that child Stanley?
Stanley: No.
Gabriel: You disappoint me, it's the greatest good.
Stanley: Well how about 10 innocents?
Gabriel: Now you're gettin' it, how about a hundred - how about a THOUSAND? Not to save the world but to preserve our way of life.
Stanley: No man has the right to make that decision; you're no different from any other terrorist.
Gabriel: No, you're wrong Stanley. Thousands die every day for no reason at all, where's your bleeding heart for them? You give your twenty dollars to Greenpeace every year thinking you're changing the world? What countries will harbor terrorists when they realize the consequences of what I'll do? Did you know that I can buy nuclear warheads in Minsk for forty million each? Hell, I'd buy half a dozen and even get a discount!

The characters in most of these movies are also presented with hard choices to either sunk lower than they already have, to the point you can't turn back or resurface back on top because you have a conscience. In the movie, Scarface, he makes a good example when he refused to help the assassin to kill the reporter's family.

Vigilante films make good examples, like The Brave One, with Jodie Foster. The character descend deeper into the world of vigilantism where she thinks she can't return back to her normal life. Another film, Death Sentence, by Kevin Bacon, makes another good example.

In the end, most Gangster/Crime films usually comes to one point of the show, making easy money without the restraints from the law of normal societies and be set for life. Variable reasons, either they screw up in their past lives by making a mistake and cannot make a decent future or their lives are already a mess to begin with and a chance to live again is presented, either way, there's a lot of reasons, including revenge. Blood Diamond, Formula 51 (or 51st State) and Inside Man.

Hope this long summary helps.