We did the American-Canadian tour, which lasted from about 9 am to about 3 pm. Our guide was Eduardo, who was well organized in keeping our group informed about what we were going to see, how much time we had at each destination, and keeping things moving. The falls themselves were impressive (I hadn't seen them before), and I was entirely pleased with the day.
A word of warning - we were told the boat ride would be wet, and it was. The Cavern of Winds, however, was much more so; any part of me not covered by the poncho was drenched!
We had a shopping bag full of souvenirs which we accidentally left on the bus at the end of the tour. Eduardo talked to the other passengers, determined it was our bag, called, and arranged a meeting time and place near our hotel so we could pick it up. Over and beyond the call of duty!