It's definitely not worth it for tourists with limited time to come here. We found the ice skating rink early on but couldn't find the actual shopping area for a solid, exhausting hour. The underground "city" is very spread out, and the shopping options, when you eventually find them, are the typical stores you can find in any mall in Mississauga (or you know, anywhere).
The signage was very limited and unhelpful, and certain (non-Eaton centre) areas were pretty deserted on Sunday around 1pm.
During our frustrating hunt, I opened up Yelp to see if others had tips on how to find the place and found several reviews mentioning that it is difficult for tourists to find. This is what I get for not checking Yelp first!