Core mechanics:
Gangsters vary from very tough Torpedoes and Enforcers down to Punks, who are about as good as you'd expect. Each character has a stat line ('Fists' 'Gats' 'Stunts' 'Smarts' etc), each ranging from 1 (terrible) to 5 (excellent), and most tests demand an equal-or-less roll on a D6, with some modifiers. Characters also have 'Skills', which may be good, or less so. Yes, I know that 'drunk' and 'gimpy' don't really constitute skills.
Mad Dogs is driven by a card deck system using regular playing cards, which allow either 'All figures' or a smaller group to activate. You can hold cards instead of playing them, then use one to interrupt the game sequence – that way, I can hold you up and Talk Big on my turn, knowing that I have a card that lets me shoot you if you don't do what I want.
On your card you can move, shoot (or both), hit with brass knuckles, drive a car badly, intimidate the locals and whatever else you like. One card allows you to move civilians so as to obstruct other players.
The basic rules are as easy as I could make them, since fast flow and lots of Cagneyesque chatter is more important than the difference between two kinds of similar revolver. Likewise, the campaign rules are about setting up scenarios rather than running an illegal business that will funnel money towards your retirement in Miami beach.