For those even mildly interested in J-pop, just download it and give it a try. The link is right there, so why not?
I do agree that her music is the least pop out of the Japanese divas as Sir.Frost said but that has nothing to do with the quality of music. It wouldn't hurt to give it a try
So what kinda of genre are you interested in overall?
Ayumi Hamasaki is extremely versatile and does everything, but you'll find most of her discography is rock focuses... and I'd recommend you start on one of her EP's so you can get a taste... so maybe download Memorial Address. Ayu has a unique voice too!
Koda Kumi is amazing, she has beautiful ballads which never get old and a lot of sexy RnB tunes. She also covers a range of genres but she mainly devotes herself to RnB
Namie Amuro is the hip-hop queen in Japan.... I'm not into Namie as much as the others... but as SO.UNCOOL. He knows everything about her.
Utada Hikaru is maybe not the best to start with... She has great songs, but her music is the less 'pop' out of the ones above.
Other mentions are
BENI - RnB female artist with a lot of cheerful cute tracks
Mai Kuraki - She slightly follows in the roots of Namie...
Hope you found that useful
EDIT: I'm slightly tired. I would love to expan on what I have said... but I don't want to ramble on.
theres also crystal kay who has a very versatile sound as well. ranging from pop to Rnb
I've always loved Utada Hikaru, but when trying to get people into J-pop, I stay away from her because her later album get more experimental. Most people I know are standard pop listeners, so I see how she could shy people away from Japanese music.
I know exactly what's going to happen once I listen to the new songs: I'm going to end up re-listening to her entire discography because I always do that when someone releases a compilation.