I was lucky enough to be there last year - lucky enough because it really is a fantastic experience IMHO. Corcovado - the statue of JC on a hill overlooking the city - is probably the single most amazing place I've ever been -- and I'm an atheist! Was staying in Copacabana which is a huge, beautiful beach, and a strangely overcrowded, faded place to live. I spent alot of time with a friend who lives in Flamengo was able to show me much more of the city and it's people. Including - don't ignore this - football at the Maracana. There's lots more, and Brazil is a huge country with enormous amounts of things to see. Please don't be put off by tales of violence - though do take the kind of care you would need in any big city. Ditto the poverty - it's there, don't ignore it, but it exists with or without you so don't let it stop you going there. As far as costs for the tourist - it's pretty cheap,and problems with ther Brazilian economy now mean the exchange rate will be working in your favour.
Having said all that -- my wife didn't like it much at all. Said it reminded her of Birmingham!