We did love the place we stayed. John, at Secret Garden Igauzu, is an amazing host. The breakfast (toast and homemade jams) was awesome, the coffee was great, and the nightly (required) chats over drinks and apps were lively.
The falls were also beautiful, though crowded and had bad food. Go early in the day, pack a lunch, and do the boat ride under the falls. It's short, but fun. And you do get soaking wet. Wear a swimsuit!
One of my favorite things about the falls was the amazing variety of butterflies. Also, they were very tame and willing to hop on for a photo op...
One thing that we didn't do in the area is to see the falls from the Brasilian side. Americans need a visa to go, and you have to get it in advance. We actually tried to sneak over with a driver we trusted but were denied and our poor driver got questioned at the border! Apparently going renegade style usually works, but not so much for us.