Perhaps if I had visited in the winter I would have been more impressed.
The underground city is interesting to me as we don't have them in Vancouver, however it is essentially a series of connected malls (and the University of course), and offers the same stores with shameless repetition. There are limited stores which are not chains, so if you are visiting from anywhere in Canada this will not offer a unique shopping experience with few exceptions.
The food courts were however handy for quick bites.