We took the Historical River Cruise.
Unless you have a particular interest in the Mississippi, the trip itself is not really worth the fare. We steamed downriver for about an hour, spent another hour at the Chalmette battlefield, and then steamed back. That was it.
The shoreline of the river that the tour passes is not very interesting: mostly a collection of shipping wharves, dilapidated factories, abandoned piers, pushboat barges, a couple of Navy ships, and a huge sugar refinery, most of which are obscured by the levies anyway. We passed the French Quarter, but it was so far away that St. Louis Cathedral was little more than a silhouette. The battlefield was interesting, but we had only an hour there, and a fair amount of that time was spent getting on and off the boat.
So why the 4 rating? The narrator, Charles. His presentation on the way to the battlefield was an excellent capsule history of New Orleans and the lower Mississippi, and on the way back he offered an optional but moving account of the events surrounding Hurricane Katrina. He made the trip worth the money.