Chances are if you have a shopping mall by you, you've got a better selection of stores selling items at prices that are cheaper than what you will find on Rue Sainte-Catherine.
For all those that say this "attraction" is a must-see, I would suggest that you need to expand your horizons as this clearly falls into the "must-not" category of things to do while on vacation. This street is dirty, it smells (like garbage and urine), is somewhat depressing/run-down in parts and I certainly didn't travel all the way to Montreal to go shopping at Foot Locker, mobile phone outlets, pawn shops or whatever other stores I could find locally and without having to pay Montreal's 15% sales tax.
Make no mistake; this is not Oxford Street in London or Newbury Street in Boston. Instead, Rue Sainte-Catherine is as unremarkable as it is underwhelming. Spend your time and money elsewhere, as Montreal has so much more to offer.