I have not seen so much of these type of movies but I think _Dog Day Afternoon_ is a representative that coming back from Vietnam as a veteran was a very hard life situation.
As in the _Taxi Driver_ Sonny and Sal couldn't cope with the burden to reintegrate to the society and take a decent profession. Okay, at least _Travis Bickle_ tried this, just failed, but that's just a side note.
However, Sonny and Sal have thought as their only chance to live after the war an honourable life in America to rob a bank. Sonny who was the smarter one, has not panicked after the realization that they couldn't become wealthy from the cash in the vault. He knew their only chance not to face repercussions is to elope from the country. They only kept hostages and made themselves as prisoners for their own good and the hope of their freedom. It's so exciting and tense to see if they succeeded and manage to escape from the country or their other plan also fails.
I also haven't seen so much _Al Pacino_ movies, but in my mind his characters are adjacently mad and assertive figures and here he is just an ordinary man whose life went awry in the war. I need to mention the bank manager and his don't give a crap attitude which was fun to watch.