The atmosphere is comparable to the Carnegie Deli in NYC, i.e. tourists, and only tourists, standing in line. But don't let that deter you, because the food is straight-up Katz's in NYC, i.e. fantastic, no-frills meat sandwiches in less-than-fantastic, no-frills surroundings.
Whatever you do, for God's sake, don't stand in that line. Order from the to-go counter next door, buy a Schwartz's tote bag, and schlep the whole delicious mess across the street, where someone has created a communal terrasse out of a shipping container.
Eat your meal while listening to the nearby accordion player run through his repertoire of unidentifiable but atmospheric songs, and give him a nice tip when you're done. Bliss.