I visited the Iguazú waterfalls twice.
First time was in 2004 and second time last October 2006. The only difference between those two trips there was the amount of water. Last year there were problems with the lack of rain in the area but finally the rain arrived and the waterfalls had about 70% of the usual water. The pictures I post are mostly from this last trip.
There are some options when you visit the waterfalls.
1) To see the Devils Throat which is the deepest fall of all and it is very, very impressive.
2) To walk the Upper Circuit
3) To walk the Lower Circuit
4) To see the waterfalls from the Brazilian side.
To see the Devils Throat you can walk a long path or you can take a little train to arrive to the place must faster.
This short trip of about 10 minutes is free. The only problem taking this train is that you may have to wait about 45 minutes to board it depending on the time of the day (and I suppose that depending on what time of the year you are visiting the park too). The place is visited by many people so it pays off to visit the park as early as possible in the morning!
The other options (Upper and Lower Circuit) will let you see the rest of the waterfalls and they are also a must but take into consideration that the place can get very, very hot so you may consider to drop one of them according to how fit you are and how good is your mobility.
You are probably asking yourself, what´s the difference between the Argentine side and the Brazilian side. Well, a guide put it very clear. When you see the waterfalls from the Brazilian side it is like watching a football match from the best seat available. When you watch them from the Argentine side, it is like playing that football match yourself.
If you, like another member of this forum said, have to pay 100 $ in order to enter Brazil or if you are short of time then my advice is to drop the Brazilian side. But if you can then give it a chance because the scenery is truly World Class. No more, no less :-)
I post a few pictures with some of the animals you can have the chance to spot. But the truth is, that with all the people in the area and the helicopters flying regularly above, most animals retreat deeper in the jungle and you only will spot them in the tourist guide :-)
If you are interested in butterflies then you can be sure that you are in for a treat because there are butterflies all over the place.
I will try to post some video clips too. They aren´t good enough as I took them with my phone but it may give you an idea of how vast the area is (2.5 miles wide).
Finally remember to wear light clothes and have plenty of water with you. We were picked from the hotel already 7:30 in the morning in order to avoid the strongest sun at "siesta" time in the afternoon (and to avoid a long quew at the train, as I said before).
You can buy beverages all over the park and there is a big restaurant serving mostly fast food.
There is also the option of driving through the jungle about 8 km and then sailing on a small boat to come very close to some falls. This trip costs about 30 $. I didn´t try it.
Once again: this is a World Class attraction! There is no photo or video that can show how impressing and beautiful this place is...