Kanye and Rihanna are the 2 biggest game changers in their respective fields. They don't get enough credit because of their attitudes.
Rihanna is a sweetheart IMO. She seems like the friendliest and most down to earth/personable popstar. Kind of like Old Britney. I think Madonna fits the attitude thing better. Alot of people overlook the music and dislike her because she's a bitch which I guess I can understand.
Rihanna started the urban trend (TTT) and the dance trend (SOS, DSTM). Diamonds and Stay were very relevant to what she was feeling at that time, her grandmother dying and the CB heartache. I don't think she was in a happy place.