Normally I try to avoid big cities on my travels, if I have the choice. But sometimes, you just cannot choose. Big cities usually serve as hub for airplanes, buses or trains, and even if you hitchhike, it´s always easier from/to the bigger cities.
So, if your next airplane, bus, train or car brings you to Rio de Janeiro, give it a chance. Don´t hesitate to spend some days here and explore the city. You´ll see, in the case of Rio de Janeiro, it´s really worth it.