Be sure to get on one of the smaller ships. We ran into some people who were on Carnival's Liberty and they were not able to enter the locks since the ship was too big. We were on RCI Brilliance of the Seas which was as big as they would allow in (106' wide and the canal is 110').
We enjoyed Brilliance. Food was so so though. I dont know if she does a complete transit though (we only did Gatun Locks).