J-Rock stands for Japan Rock and within this genre you'll find several completely different styles. Both in music and in clothing. I'll inform you about two of them.
Oshare Kei is a pretty light and joyful style of music. The lyrics often go on about love, life and the different kind of problems that all out of sudden can show up. The members of the OK bands often seem very lightheaded and crazy. They often wear smaller clothing, multicolored hair (Miyavi is a good example) and lighter make up than the Visual Kei'ers. Colors and a wide smile is the trademark within Oshare Kei. You may not even like Japanese music, but the feeling that occurs under an OK concert is impossible to resist. The members of the group often throw jokes with the audience in-between the songs and jump all around on stage while performing.
Typical Oshare lyrics may go something like this (Bond ~ Kizuna by An Cafe):
Count on your fingers the things that are truly important and needed
In the end, the important things are few
What's left, is generally unneeded trimmings
People hurt and are hurt
You recognize, the first time you've been hurt, right?
As long as the long silence continues, you'll still be afraid of being alone
Someone who can't even protect the bonds they have tied, is a powerless and monotonous living being
Even though the lyrics are quite depressive, the melody almost always speed up with a happy tone.
Some examples on Oshare Kei bands are
Read more about An Cafe here: http://seeandlisten.wikidot.com/antic-cafe
Visual Kei bands often focus a lot on the costumes and the make-up. Visual Kei is like the Japanese form for boy band since the fans are mostly girls. But the music is much harder than the regular English boy band style. Some VK bands go in for screaming, growling and banging ahead on the drums, while other has a quite good vocal and rhythm. Heavy make up, dark, complicated clothes and a gloomy stage performance is the feature for this music genre. In contrast of OK, most VK bands have a very gloomy apperiance.
Typical Visual lyrics may go something like this (Bathroom by GazettE):
I want to fall asleep, just feeling the fear of awaking.
I want to forget everything. It is selfish nonsense.
I call your name. I go mad with the silence.
I shouted while holding your thin shoulder. It was too frail with warmth.
Some examples on Visual Kei bands are
Read more about the GazettE here: http://seeandlisten.wikidot.com/the-gazette