Rio is really nice... I've been there four times, last being this past January, and I feel like a local during every visit. I speak portuguese fluently, so that helps. People are extremely friendly and helpful. One thing is, just skip the expensive jewelry and anything to make you stand out, and you'll be fine. Situational awareness is key here too. This is not a place to be walking down the street and looking at your phone, unaware to your surroundings. Snatch and runs are quite popular, with people whom aren't always alert usually being victimised.
Check out Corcovado: Cristo Redentor... Views are AWESOME. Take a cable car ride between Pao Acucar (Sugar Loaf Mountain's) "loaves." Take a stroll along Ipanema, Leblon and Copacabana beaches. Visit O Jardim Botanico in Leblon/Botafogo where you get really tall trees and beautiful plants, and EXCELLENT shade during the summer months. Visit the Escadaria Selaron (Selaron Stairs) in the favela, where it's a stairway that's fully tiled. You see a lot of Lisbon history here, as well as the African heritage brought to Brasil by Portugal back in the day.
With that being said, stay out of the favelas at night. The local police are not allowed in these "ghettos" and Federal Police only can come in at certain hours, to make sure that peace is maintained. Also, if you are brave enough to drive in Brasil, remember, traffic lights are just devices with a pretty red, yellow and green lights.

Red means optional stop and yellow means go faster.
Taxi's are state regulated, and are cheap as hell and are in abundance. Not all of them accept credit or debit cards, so make sure you ask before jumping in. An EXCELLENT app to have is 99Taxis. This allows you to hail a cab to your location, and pay with a card. It's kind of their version of Uber, which is BANNED in Brasil. The Reais, which is their monetary unit, isn't doing very well, so a US Dollar goes really far. You can get about three bags of groceries for about $9.00! I hope all of this helps.
Tenha voce um boa viajem!
Tchau,
Sean