I've never been to Chicago and I also haven't generally been impressed by deep dish pizzas. Giordanos changes the game. Hands down the best deep dish pizza I've had. We got a simple one with just spinach and pepperoni but it was honestly all we needed. There is just so much cheese in this pizza that any more than 2 or 3 toppings and I anticipate it would be too heavy. One meat and one veggie was just enough for us to be able to taste all the flavors of the pizza. I think my actual favorite part was the crust though. It was nice and crispy.
The only thing to be aware of is they make your pizza to order, so it can take about 45 minutes. You should plan on coming when you have plenty of time.
For someone like me who hasn't had much other deep dish Chicago style pizzas to compare to, I was pretty impressed.