I finished this anime this morning and really enjoyed it, but I do have a few things to say.
This review contains no spoilers. :)
Story: The story, which overall wasn't that bad, could have definitely been fleshed out more. There were a lot of plot twists, especially towards the end, which I guess made it more fun to try to guess what the relationships between characters were. I thought I had the story mostly figured out towards the beginning of the second season, but the longer I watched the less sure I became. The downside to this was that there was almost too many plot twists and the last few episodes seemed to be really rushed. If the writers had crafted a simpler story then it would have fit nicely into a 24-episode bundle, but unfortunately, it felt like they bit off a little more than could be easily digested in such a short time span.
But putting aside the size of the plot, I liked how there was a specific thing that the characters were working towards. I saw that another user compared Nurarihyon no Mago to Inuyasha (which incidentally is one of my favorite anime,) and while there are a lot of similarities, something that Nurarihyon had that Inuyasha didn't have was a manageable goal. Instead of wandering Fuedal Japan, fighting monsters and trying to round up all the tiny pieces of a shattered jewel, the characters in Nurarihyon are simply trying to avoid the destruction of Kyoto. While the antagonist is still quite powerful, the target of Nurarihyon is something that can eventually be achieved, and the anime pushed towards the objective at a rate that is admirable. There are no filler or extra episodes, and almost everything (even the often random plot twists) is relevant to reaching the destination of peace in Kyoto. Because the goal of the anime was something concrete and relatively simple, the conclusion was quite satisfying. Watching the anime, I found myself thinking that I would hate the end, but I was wrong.
Animation: I thought the animation was great, but this could be because I've watched a lot of older anime. If you put this anime up against something like Inuyasha or Heroic Age, it would come out on top every time. I won't say it's as good as Sword Art Online or even Noragami, but it is well done.
Sound: The sound was very good. I liked the intros/outros, and the soundtrack to the anime itself was great. I was pleasantly surprised by its quality, and how the anime's creators utilized sound and silence equally well. The moments that I feel illustrate this the best occur in the last two episodes of the series. During the final boss battle, all the characters rally behind one single leader and the soundtrack kicks in with a groovy rock theme reminiscent of the intros. If you listen to the entire anime carefully, you can hear the same theme occurring in other places. This lent a feeling of cohesion to the anime as a whole and a sense of importance to the specific scene. Later in the anime something tragic happens in the middle of the final battle. Suddenly, all of the background noise of the fight ended, and all we were left with was silence and no choice but to focus on the character on the screen. Once again, a masterful way to create a sense of gravity in a scene.
My only complaint for the sound was in the dubbed version, where I found many of the actors' voices irritating. This is really just a problem I have with dubbed anime in general, and Nurarihyon isn't to blame for it. Many people would probably disagree with me on this point, and since this anime's dubbing wasn't the worst I've heard, don't let the possibility of irritating female voice acting deter you from watching this show!
Characters: I loved the characters in this anime. There were so many wonderful ones with so many wonderful backstories, and I wish that we'd had 24 more episodes to get to know them better. The designs and original voice actors were consistently great, and I did not encounter any that I hated. Even the antagonists had good reasons behind their actions, and it was difficult for me not to sympathize with them. I believe that if your audience can sympathize with even your most notorious villain, you’ve done your job as a writer, and the only thing I would change about the characters is to give them more time to become even more likeable.
Overall: Overall, the anime was great. I would recommend it to anyone who is interested in anime about traditional Japanese mythology, onmyouji, or yokai. It’s not the best, but it is one of the better. I enjoyed it, and will continue to be interested in the Nurarihyon franchise. Give it a shot; you’ll like it or you won’t. Either way you’ve lost nothing, and might have gained a new show to watch. If only it were longer!