Simply the best coffee in Rio. Nothing more needs to be said, but I'll say a few more things anyway…read more;P
As you can see from the other reviews, you pay what you think is fair. There is a ton of information on the chalkboard, but basically they tell you what it costs in materials, and what it costs them to keep the store going (labor, rent, utility bills, etc.) They also tell you what their budget is for the month, and how much money they've taken in.
Don't expect anything fancy. There isn't any place to sit down and get some work done. There is only one bench along the wall, and it's usually full of people. There are some condiment tables where you can add sugar, chocolate, cinnamon, etc. to your drinks.
Definitely come here for your coffee if you are in Centro. It's in a kind of weird location - right at the top of the escalators if you enter the building on the side of the park.