We did the very same Panama itinerary in December on Celebrity Summit. We did 10 days on Mercury (Mexican Riviera) two years ago also, so are familiar with that ship. Although the Summit is a bit nicer, you will have a great cruise. We loved the ports, especially Cartagena (don't listen to the scare mongers that tell you to stay on the ship in Columbia. Go on a tour!)
This was our first full transit Panama but had dgone in the Atlantic locks before. It is worth seeing, but takes a good deal of time. Expect some jostling and rudeness if you want to get a good spot. You can see just fine from ie. the Promenade deck and take it easy, while everyone is fighting for position at the bow. By the time you have passed through all the locks the crowds have tired and dispersed. We were eating dinner in the DR before we were through the last lock.
My husband's only complaint was that there were too many sea days and he got a bit bored.