You know, I've been watching FotNS and while it's not bad, it is really repetitive. I mean, I like the show and all...buuuut, it's main draw is it's grit and crazy fights. And even the grit can be over the top sometimes. I mean, how many episodes does it take for a certain character I'm not saying because of spoilers to die. I think the way every episode ended was him looking at that star and saying "Well, one day this thing will kill me."
Yeah, HOTD is not a serious anime. That's not even supposed to be why people watch it.
FMA:B is fairly serious but also is fairly comedic (though that definitely slows down).
I think Shiki (WITH GACKT-SAMA!) is....well, I don't know if it's a hit, probably not, but it is the latest thing that I find fairly serious and I think it's a good show.