Brazil is probably the most biologically diverse country on the planet. It has the biggest rainforest in the world. It has the biggest freshwater wetland in the world. What else do you want? If you are a biologist, naturalist or wildlife enthusiast, you just gotta go....
I travelled Brazil for a month in 2014.
The main language in Brazil is Portuguese. Yea, so you have learnt all that espanol for travelling around the tropical Americas. Not much good here. Some of the written stuff is similar to Spanish, but the pronunciation is very different. No rolling 'rrrr's' here. I managed to bumble around with minimal language, and these days you can have some handy language apps on your smart phone just in case you are stuck.
If you are used to the cheapness of tropical travel elsewhere, particularly south-east Asia, Brazil comes as a bit of a shock, as it is not as cheap. The cheaper options, such as backpackers accommodations, are not always good. And the more popular places, such as Rio and the Amazon, are pricier. So you end up spending more money than you probably planed. The currency is the real (although being that in Portuguese nothing is pronounced as written, so it sounds like more like 'nngeal'... or something).
There are some famous spots that are worth visiting, and lesser known areas that need to be explored.
The capital is Brasilia, but the most famous city is Rio de Janeiro. This is one of the prettiest cities in the world, with some good natural areas, including Sugar Loaf and the Rio Botanical Gardens.
The most famous natural area in South America is of course the Amazon. Most of the Amazon is contained within the country of Brazil. There are various options for accommodations and tours here. Many tourists go via the larger city of Manaus, near the Rio Negro. When there I stayed at Antonio's Jungle Lodge.
One of the most spectacular spots in Brazil is Iguassu Falls. The falls themselves are great, but the surrounding rainforest is beautiful.
By far the best wildlife experience in Brazil, and one of the best in the world, is the Pantanal. It has incredible birdwatching, and other great animals and plants, and good lodges. I stayed at two lodges, including the Hotel Pantanal Mato Grosso and Pousa Alegre.