The tour I took was the Eco Tour of Gatun Lake plus Locks. The lake portion was so-so (word of caution: depending on your boat driver, sit on the right side – if you’re on the left you’ll spend the excursion looking at the lake and not the shoreline where birds, plants and wildlife are). The visit to the locks was very interesting – especially getting the landside view prior to the Millennium’s transit the next day. One barge and one freighter were passing through Gatun locks while we watched. If you can get an excursion that takes in Gatun locks you should. I cannot recommend the Gatun lake eco tour portion though.
The Fortress, Dungeon, Inquisition Palace tour was pretty decent, even on a very hot and muggy day. A word of caution – to climb to the top of the Fortress takes a while. It’s a steep climb. Our guide was knowledgeable and clearly understandable. The old dungeon is now a marketplace so this was really not much more than a shopping stop. We did, however, enjoy a nice walk along the cobblestoned streets on the way to the Inquisition Palace. This space got very crowded with 3-4 tour busloads of folks vying for space and a view. Still, recommended for some good history of old Cartagena.