I agree that the Panama Canal is a "one of a kind" trip. We have been to Panama three times; full transit, partial, and just docked at Colon 2000 (ship never entered the Canal).
The full transit visit was by far the best, however I realize that it is difficult for most cruisers to be able to do a full transit cruise. Therefore, if you do a partial transit, be sure to take a tour that lets you see the entire Canal including the Pacific side. A partial transit just goes into Gutan Lake and then back out covering about 5 mles of the 55 miles of the entire Canal. Do not miss the other 90% of the Canal, not to mention seeing more of the country.
05/89 NCL, Seaward, 1990 Carnival, Topicale, 1991 Carnival, Festivale, 11/93 Wind Star, Wind Song, 01/95 Celebrity, Horizon, 01/96 Celebrity, Century, 01/00 Celebrity, Zenith, 01/01 Princess, Ocean Princess, 01/02 Princess, Ocean Princess, 01/03 Celebrity, Summit, 05/04 Princess, Diamond, 01/05 Celebrity, Galaxy, 01/07 Oceania, Regatta, 01/08 RCCL, Voyager of the Seas, 02/09 RCCL, Voyager of the Seas, 01/10 Celebrity, Solstice