Mom and I were there last year (while cruising on the Liberty). We were there on a Sunday and essentially all the shops were closed. The Croisette (road along the shore) was neat with the hotels and hotel owned beaches. We were up on top of the hill at Le Suquet (the tender drop off is at the harbor below this hill) and it was good place to look down at the city. Found some familiar names (e.g. Sharon Stone) in the garden in front of where they have the film festivale. Overall we were not very impressed. Even if the shops were opened, they were quite expensive, and carry many items one could find at any number of big cities (NYC, Paris, etc, but at higher prices in Cannes).
If I go back (on a cruise) I would take an excursion to Monte Carlo, or Nice, or the country side outside Cannes.