Ryuuguuden is a VERY weird read. Does weird = bad? No.. but just be warned.
The weirdness of Ryuuguuden, otherwise known as Castle of the Dragon, comes from it's trippy, hallucinogenic, bizarre, and even somewhat scary premise. So it's about two boys who follow a girl onto a penis shaped train which dives into the ocean and arrives at a sea brothel. Yeah, it's something else. With all this said, you shouldn't let this premise fool into thinking it's going to be some ecchi or purely erotic rubbish.
The direction the story goes at multiple times is often highly creative and interesting, such that you'll
often be left greatly surprised at certain conclusions. The changes in tone throughout the series are also quite unique and offers a refreshing blend that keeps things from being stale.
Often cartoonish, yet at times gritty and somewhat realistic, the art in Ryuuguuden is very impressive, especially given that the author of this series has only worked on a few other one-shots previously. It's unique and has a lot of personality to it, similar to other well-known artists that have their own style.
There are two main protagonists in the series, Anni and Bo. I didn't love them, but I don't think we're supposed to. They're each flawed and juvenile in their own way. They annoyed me at times, but the story wasn't ruined. There is also an antagonist. He's just a little insane, but it works. If only the story gave his thoughts a bit more attention.
All in all, this is really something else. If you have an open mind, you'll probably find something to enjoy here.