As for Our lady of Aparecida, you can go to this wikipedia link (I know it's not the best of sources for many things, but it tell the basic story concerning this Brazilian devotion): http://en.wikipedia.org/wiki/Our_Lady_of_Aparecida
And for how Catholic is Brazil ... that's a complex question. True, we are the largest nominal catholic country in the world. But most catholics here also have a deep foot into sincretism, kardecism, new age, you name it. Brazil is a huge country and a 2 hour drive from one city to another will give you different Portuguese accents, even different cultures altogether. I live in a very well planed city http://en.wikipedia.org/wiki/Curitiba , not as poor as most Brazilian cities. Quite the contrary. But I will dare to say that the practice of our religion is pretty much the same throughout the country. It's hardly traditional, mainly because of the terrible "theology of liberation". It had a huge impact on the liturgy, devotions, clergy, everything. It's quite sad. Yesterday, I bet most priests talked about "Jesus came to free us from the oppression of the powerful" kind of thing. I have to say, though, that you can find wonderful priests, maybe not as traditional as you can find in America or Europe (except for the Campos priests, I guess). Here in Curitiba I am fortunate to have an old Italian priest with sound theology and also a Monsenhor (Spelling?) who celebrates the NO De Angelis with gregorian chant and also teaches sound doctrine. If you count the number of Brazilians who actually go to Sunday Mass, we would not be the largest Catholic country in the world.
I have to say though, that Brazil also has a great number of simple people who have a love for Our Lady that is strong and beautiful, a devotion to the saints that is touching. Let's hope the sects won't destroy it.