If you go to New Orleans, there are a few things you need to try...gumbo, jambalaya and of course a po-boy. The reality is that a po-boy is just like a sub, but that's not important. What is important is that Johnny's has a pretty mean po-boy.
When you are looking for something quick while walking around the French Quarter, try Johnny's. It is a very simple, diner type place. You seat yourself (if you can find a table) and order at the counter. The specialty is obvioulsly the po-boy and you can find some interesting combinations. I had the crawfish po-boy and liked it very much.
This place is worth going to just for the atmosphere. People stuffing their faces, dripping po-boys, an open grill, etc.