I absolutely adore this place. It's a block from my work so I frequent this place at least 1-2 times a week. The atmosphere is fun and makes you feel transported to old time Chicago.
While this place can get busy at lunch time they know how to handle the crowds and it normally goes pretty quick even if the line is super long. I recommend ordering ahead on the app as well which makes things go by pretty quick.
Some of my favorite items are the Combo sandwich(sliced beef with a sausage link), the bacon cheeseburger, their hot dogs and chicken sandwiches are fantastic as well. I'm not sure I've had something from Portillo's that wasn't good so give just about anything a try!