[bondingo]

Like:
Ayu - my favorite
Shiina Ringo - amazingly unique voice and she's so creative
Koda Kumi - wonderful voice, catchy songs, and I like her sexy image
Namie Amuro - I actually like her music from LOVE ENHANCED to now more than her old
BoA - great voice, cute songs and style
Utada Hikaru - amazing voice and great lyrics/PVs/compositions
Hitomi Yaida - another awesome unique voice with great songs
MISIA - best voice of any J-Pop singer IMO, AMAZING!
(I like more but these are my favorites)

Middle:
Ai Otsuka - LOVE her ballads, but her super happy songs are a little too "!!!!"
Morning Musume - Some of their songs are just plain annoying (Mr. Moonlight, The Peace), but I love a lot of them (Shabondama, Do It! Now, Love Machine)
Gackt - I usually don't like male singers but he has a great voice, just some of his songs don't really appeal to me
Matsutoya Yumi - I'm trying to like her and I really like some of her songs, but I'm just not completely used to her voice yet

Dislike:
Mika Nakashima - GLAMOROUS Sky and Yuki no Hana are OK, otherwise, her musical style is too bland for me and her voice isn't really good IMO
Kinki Kids - annoying songs and they aren't good singers
Coconuts Musume - some of the members don't even speak a word of Japanese, plus they're annoying