Cuisine in Rio has a number of unique characteristics, especially for a Westerner that may be unversed in the ways of the churrascaria, por kilo, or the ubiquitous juice bar. Different does not mean worse, and in many cases when in Rio de Janeiro, it means better.
Typical Brazilian dishes like feijoada (a meaty stew with black beans) can be found in eateries around the city, while a large number of sushi and other seafood restaurants are popular because of the proximity to the Atlantic coast. You'll find cheaper options beyond the usual tourist avenues of Ipanema and Copacabana, but quality is generally good in these areas as well.
One thing you must try (if you don't have an aversion to meat) is dining at a churascarria. Food is served rodizio-style, meaning that a rotating (and endless, if your stomach is a black hole) selection of meats is brought to your table for your consumption. Many of these restaurants will provide a number of other side dishes with your grilled meat courses. Porcão and Marius are popular establishments.
Then again, depending on your appetite, it may behoove you to pay by the kilo. A surprising number of establishments in Rio go with this option, often offering a buffet-style service where you weigh your food before eating. This can be good if you plan on staying waifishly thin or can be pulled off pretty cheaply at joints like Fellini, Ming Ye, Plana Grill, and more.
Because of the health and man-it's-hot-by-the-beach-I-am-really-thirsty crazes, juice bars are an omnipresent option in Rio and often come with sandwiches or other quick bites to eat. These juice bars ride the coattails of some of Brazil's fruits, including acai, papaya, and guarana, and are an inexpensive and refreshing way to grab lunch or a snack. Bibi Sucos and Big Bi's are pretty much anywhere you go and are the cream of the crop.
For more information on specific places that may be found while in Rio, check out our listings or ask our community. Come for Rio's party and stay for the food!