Hi there! ^_^
I agree with lots of the recommendations already said: Dir en grey (I'm not sure that their music is really "metal"... mehh, I find those classifications so hard! their stuff is really diverse), Gazette, D, Due'le Quartz, Rentrer en Soi, Vidoll, Kra, Merry and Baroque... all good stuff. ^_^
Gackt... well, I'd describe his stuff as being more like pop or soft rock. It's pretty good but possibly not heavy enough for what you're looking for.
Miyavi is a great guitarist. *thumbs up*
Malice Mizer are a kind of hybrid goth/rock/classical... they produce some interesting stuff in a great variety, some heavyish (e.g. Beast of blood) and some almost classicalish (e.g. the Bara no seidou album).
If you like goth, you might like to try Eve of Destiny. Kozi, their guitarist (it's a 2-member band) makes solo works also, and his Katarushisu/Catharsis album is good. ^_^
Kagrra are very good indeed, I really like them. They're not metal, but they have awesome bass and... well, all the parts are awesome really!
SID are a softer rock/jazz hybrid, too, but they are DEFINITELY worth a listen - Mao has a fantastic voice.
In addition, can I recommend some other good bands:
D'espairsRay!!! They are fantastic. If you like hard rock/metal, you MUST listen to these guys! That's an order! All their stuff is good, but good songs to start off with are Forbidden, Garnet and [S]yste[M]. ^__^
The Zolge - I've heard them described as "punk" but I hear them as rock... the album Deadly Sanctuary is excellent. They are disbanded now - they were the band of the former singer of Eve of Destiny.
MUCC - I love their music.
(Those last 3 are a bit more of punk.)
Happy searching and listening! ^_^