Sorry to dredge up such an old post but I think Japanese music deserves a bit more kudos.There are so many really good (technically) musicians it's hard to ignore.You don't need to understand all the lyrics to appreciate the music.
While I can't get into most J-Pop there are a few retro style bands that are pretty awesome. Kinoco Hotel are a favorite, they do 60s/70's inspired stuff that absolutely rocks (watch for 70's Japanese movie references in their clips). The Mercies and The Neatbeats both do great early 60's/Beatles inspired stuff. ZAINICHI FUNK do some super cool James Brown inspired funk ( the band is SO Kool with a K ).The OldTones do some great Ska. Lastly there is one visual kei band I like, Exist Trace, they are an all girl band (yes, really girls) and they rock hard.
I worked in a music store for years and never knew there was so much good music in Japan,my tastes are extremely broad so I'd love to hear of any bands people are listening to.