What I am about to say is relative to Rihanna's standards. So don't go in expecting vocal virtuosity when I say she sounded really good during her massive set at Rock In Rio 2015.
It wasn't that her voice soared or done anything particular impressive. It was simply that it was up to the level required for the Diva's bevy of hits, sounding cleaner and clearer than it has in a long while.(That's not meant to read shady!) And boy oh boy did she perform A LOT of her material. And it wasn't just all singing over playback either, with songs like We Found Love being fully reworked for the show.
The crowd certainly appreciated it, being electric and engaged throughout.
(Also whoever had Sam Smith on their shoulders during Pour It Up deserves a medal and statue in their honour. They must be bordering on Hulk level strength.)