We did this cruise last year and we decided to go on the Rabat trip instead of Caseblanca, we found the guide to be very informative and enjoyed the trip. A lot of people said they did not enjoy the Casablanca tour as it was hot and very crowded and quite difficult to keep together. I would definately advise going on a organised excursion and not going into Casablanca on your own.
We went to Casablanca on a Thomson cruise in August and it was awful, dirty, smelly, not picturesque at all and the peddlars are really annoying, lots of other reviews re casablanca have said the same. I f you do really fancy going ashore I suggest you go with an organised excursion, that might be bette.