There is not much to say about Iguazu Waterfalls. Just go there and enjoy the wonderful nature. I posted some pictures for you to enjoy.
On the Brazilian side, it is enough to just go for a few hours into the park. I even stayed a bit longer that the last bus left the Park because I wanted to see the sunset at the waterfalls. You can still get a transport at the Hotel Cataratas that brings you out of the park. At the Entrance, there are still buses going to the city until 11:00 pm. If you want to stay longer to see the sunset, you just tell the guy that collects the tourists for the last bus that you stay at the hotel Cataratas.
In Argentina, there are a lot of opportunities to see the falls from different angles and spots. You should plan a whole day to stay in the park because the entrance fee is the same if you stay only a couple of hours or the whole day.
The whole place is full of butterflies and other animals like monkeys and Coatis… but they move a bit too fast for my camera to capture. Some friends told me they did not see the butterflies so they might be in season in April.
I have been at the dam of Itaipu as well… I was impressed how big it is (Next to Three Gorges Dam in Hubei China, it is the second largest Dam in the world). I think it’s not really worth to visit unless you are interested in the technical details.
(click photos to enlarge)