So, Metal Gear Rising sold in the region of ~330,000 units in Japan, and charted well in the UK (neither the UK nor US figures have been announced yet).
Those numbers are enormous when viewed in context of sales of other titles in the genre. Recently, DmC topped out at a mere 110,000 units (unfortunately) and Bayonetta, Platinum's highest selling game to-date, only sold 205,000.
Presumably, the increase is attributable to strong branding with the MG franchise. However, considering MGR received a strong critical reception this bodes well for Platinum and any potential sequel to MGR.
I'd struggle to say that it means much with regard to re-igniting interest in a 'dying' genre, given that Japan has always tended to flock to these types of games, but it's good news, regardless.
Feel free to discuss (all figures are PS3 sales only).