I did a partial transit of the canal several years ago. The ship no longer exists; I think it was Admiral Line's Azure Seas, if memory serves (which it doesn't usually). We went through the first 3 or 4 locks to Gatun Lake, and then turned around and went back out the same way.
We had seen a film on the building of the Canal a day before getting there, and then seeing it in person was fascinating. We could practically touch the locks on each side, and the ship seemed much smaller than the panamax ships today. Some day I'll do a full transit and end up in Acapulco.
Australia and New Zealand are definites on my list, too. How long a cruise was that? From where did it sail?