I used uber for the first time in Rio De Janeiro and it was a great experience.
The city had experienced a lot of rain and taxis where nowhere to be found. even with 2x surge pricing, the cost of the uber was much less than a cab. The only issue was that I don't speak Portuguese, and I had one driver call me and start shouting at me in fast portuguese even though I told him upfront I did not speak it. I noticed there was an UberENGLISH option but no cars were available for that. My second Rio UBER experience was perfectly fine. I actually liked it better than a taxi because I didn't need to carry Reais, and didn't have to worry about being "tourist taxed"

ETA: availability was obviously better inside Rio city center, but in places like Barra de Tijuca it was much less..I did have to wait a bit for a car to come available.

Fashion Mall area, forget it - there were no ubers to be found.