There's lots to say about this waterfall. Click on one of the following links to jump to the section you're interested in...
ABOUT THE FALLS
No matter how you spell or say Iguazu Falls, it is indeed a crazy waterfall.How crazy, you might ask?
Consider a network of 275 different waterfalls spanning an area 3km wide (2km of which is the upper rim of the waterfall) during its normal flow of around 1000 cubic meters per second. It is such a natural wonder that UNESCO designated the falls as a World Heritage Area in 1986.
Sitting on the Iguazú River, it is shared by Argentina and Brazil as both countries are separated by the river. Catwalks are built on both sides providing closer (often times mistier and wetter) views of the great waterfall.
During normal flow, Iguazu Falls is actually split into two main parts by the San Martin Island (La Isla San Martín). The part with the largest volume of water is the narrow horseshoe of the Devil's Throat (La Garganta del Diablo). This is the portion of the falls that is split between Argentina and Brazil.
On the other side of San Martin Island is another series of waterfalls and cascades (many of which have names) with the main one being Salto San Martín. This side is exclusively Argentinian. Among the names of the waterfalls on this side are Salto Eva, Salto Adán, Salto Bossetti (very impressive), Salto Dos Hermanas, Salto Alvar Nuñez, Salto Guardaparque Bernabé Mendez, Salto Mbigua, Salto Chico, and Salto Lanusse. There are also several waterfalls going through San Martín Island (e.g. Salto Rivadavía and Salto Escondido; also on the Argentina side) as well.
What makes this mega waterfall so special is that it feels like it's in nature where it belongs. Sure the catwalks and jet boat tours (along with Brazilian helicopters) can take away from the nature, but it's certainly more natural than one of the rival waterfalls like say Niagara Falls.
Speaking of which, numerous catwalks afford you various ways to view and experience Iguazu Falls. Argentina has most of the catwalks while Brazil's walks mostly focus on panoramas of the Argentinian side as well as closeups of the thunderous Devil's Throat. Regarding the Argentinian catwalks, Paseo Superior takes you around the upper rim of the waterfalls Salto Bossetti and closer views of Salto San Martín while Paseo Inferior takes you to the bottom of parts of the falls while providing boat access to San Martín Island.
There are other ways to experience the falls such as a thrilling boat ride, which you can read more about here.