It's the only "Pittsburgh thing" I really knew about beforehand and it didn't disappoint.
Seems to me a lot of the negative reviews are from people who built this up too much. Yes, it's famous, but ultimately it's a just a lunch meat sandwich with fries on it. Enjoy it for what it is.
I went with pastrami and it was solid. Definitely left full and hey, now I can say I've been here. Worth the trip.