She was the first J-pop artist that I was really into. Amongst the other artists, I think her voice is much better than 90% of other and more popular acts.

She's popular but not as popular as others. Part of the reason is because she very rarely does live appearances on shows that are designed to sell the artist (Music Station, etc). She does do her own events and has a radio show I think. My info may be outdated, though, since she's not huge amongst English-speaking J-pop fans and because I haven't been keeping up.

I do know that in the beginning of her career, she was known for her trademark ponytail hairstyle but has since changed to a more mature look.