The arts stuff is pretty neat.  although a bit less structured than fighter creation, it seems.  

About the only thing I can see is I hope there's a major discipline for summoning shikigami and the like.  Because it's fun, pretty much. And a relatively big area in onmyoudo, so it'd seem appropriate for something people could do.  

I'll have to think about what sort of character I'd like to play.  I've got a few weird ideas, but nothing too concrete.