I went to Brazil but for Salvador carnival. Carnival is a great experience and going with the band at least once is something I would recommend. Now from what I've been told and seen of Rio Carnival it is not like Salvador at all. The main event that everyone goes to see or raves about is the parade of the samba bands in a huge stadium. And it is literally that. You sit in seats watching all the bands go by. There is no interaction or getting involved at all, whereas Salvador carnival was like Notting hill carnival in that it's on the street and you can get involved. I do believe Rio has a smaller street carnival so you can still get involved but it's not to the scale of Salvador.
Word of warning is be on your Ps and Qs when out and about because assuming it's like Salvador during carnival, muggers and pickpockets are in full force and they normally roll in gangs more than ready for the swingers. To give you an idea, virtually everyone in our hotel barring my friend and I was robbed during the 6 days or so of carnival. If you have some streetsmarts about you you should be able to identify the potentially dodgy characters and move to reduce the likelihood of ending up in a situation. Also do everything to stay our of the way of the police because they are probably the most violent gang of individuals you will come across in that entire country.
Not sure what the availability of English is like in Rio, but where I stayed in Salvador NO ONE spoke English outside of other tourists in our hotel so have a decent enough amount of Portuguese in your locker to order food, ask where to catch a taxi, etc.
All in all, I would love to go back for like 3-6 months and actually try and explore the country and get my portuguese to a fluent level.