-Writing quality : No grammatical errors, and nice style of writing.
-Updates : There never was a single day without an update, kudos author.
-Story Developement : Great. I won't expand much on the subject, lest there'll be spoilers, but all I can say is that it's interesting. Don't be turned off by the seemingly slow pace at the very early chapters tho.
It has a nice steady pace, with no bullsh*t illogical power-ups every damn chapter for no apparent logical reason.(glances at a certain Shisui Reincarnation atg fic), and everything has an explanation. Everything is logical or at least have a bit of that in it. There's no : "Why do I have this power? Because. Why does it work like that? B.E.C.A.U.S.E."
In short it's not a "wish fulfillement" type fic.
It's a bit similar to HN1F too, as the MC is not solo and has a clan to take care of too, tho it may not be THAT obvious in the beginning XD. Going by the readers reactions (and my self), I can safely say that you can expect hype :D. See for yourself for the rest :)
-Character Design : No one-dimensional characters. Characters are well portrayed, the interactions are meaningful and most importantly the characters stay true to how they were portrayed (Glances again at a certain Shisui atg fic -_-).
-World Background : Not much can really be said about this since it's already been established in atg. Tho the authors added some bits in it ;)
In short it's a great fic with a lot of potential. The only reason why it hasn't claimed it's place in the top 20/10 is that Nurarihyon is not THAT popular, so readers are not immediately attracted. They'll say something like : wtf are youkais doing in atg? I know since myself didn't begin to read this until I was VERY bored. Didn't regret this I assure you, a great read.
And tho it's fan base might be small (for now), it's a devoted one this fic has. Please spread the name of this fic for others to discover this gem.