Dunno about this, well it is her style that is mostly bothering me (i must add that i'm not at all familiar with her repertoire). Granted the game is not out yet but from the trailers I've got the impression that the soundtrack is mostly jazz and funk . A pop songmight be a bit out of place if indeed I'm right about the rest of the soundtrack.  Well guess we'll see how this song and the rest of the soundtrack will turn out soon enough.

Okay.

" Okay. "

I felt the same about the Genki Rockets, and look how that turned out :) 
 
It's alright, it is a commercial theme song, The fact is the game itself features some fantastic in game music from what I've heard already,  I really like the music in the demo's prologue level, I don't know who the J-pop artist is but it sounds cool and suits the gameplay well.
 
 The OST that's being released at the end of the month (or next) will be as big as the Okami one in size. 
  
 edit:
  
I do like the "spark that joint" bit at the start.    

The theme song doesn't really sound that great or anything, its pretty much generic J pop.