She's been singing with the right placement nowadays - her voice has been so much resonant and more powerful.
She's singing through the mask, which is the same placement Whitney was using, and the same Mariah was using during her Music Box era. Her deeper tone is due to keeping her larnyx down while singing which makes her voice stable and much more free.
She sounds good, and I've never understood why people say that Rihanna is a poor performer.
I mean, she's not phenomenal or anything, but I still think her talent is at an acceptable standard.