Unfortunately, Haiyore Nyaruko-san is one of the latter.
The anime takes place in a world where deities of the Cthulhu Mythos are secretly wreaking havoc on Earth, often having their horrifying appearance and demeanor replaced by that of a cute teenage girl... or boy. After the titular Nyarlathotep arrives on Earth to save Mahiro from a sudden alien attack, she chooses to stay at his house after deciding that she loves him. This, of course, confuses our dear protagonist and gives precedence to his tsundere behavior.
As the episodes pass more deities begin to work their way into Mahiro's treasured and so-claimed "normal life". The first of which is Cthuko, a twintailed and obsessive bisexual incessantly chasing after Nyaruko and her body much like Nyaruko does with Mahiro. Hastur also makes an appearance, a young boy who looks very much like a girl and frequently causes confusion to Mahiro as a result of that. Other characters include Mahiro's mother, secretely working as a deity hunter, and Ghutatan, another deity in the form of a small girl that joins in on the shenanigans for the final two episodes.
Calling any of these characters interesting would be a gross overstatement.
These are one-dimensional and stereotypical archetypes that do little except fulfilling the audience's penchant for attractive young girls. Most of the interaction between them revolves around the same repeated jokes and situations, used again and again with not a single care for change. Nyaruko will behave in a forcefully lewd manner towards Mahiro, often involving sudden kisses or talks of marriage, and then he'll become angry and stab her with a fork. Cthuko will go on to do most of the same towards Nyaruko and she'll push him away because of her love towards Mahiro. After seeing this interaction repeated for the nth time it becomes incredibly stale and tiring. It really makes evident that there is nothing going for the characters besides their physical appeal, and Xebec frequently exploits that and uses it as its way to catch an audience.
In between all the awful character interaction there's an abundance of superfluous otaku references. These include dozens upon dozens of titles such as Back to the Future, Ichigo Mashimaro, Ashita no Joe, Denpa Onna, and Haruhi. Now, references to other anime can be amusing and add to the comedic value when they're implemented well but that's very far from being the case here. There aren't just a few thrown in during each individual episode, but rather dozens of times in each, sometimes flipping from one reference to another in the span of about 15 seconds. There's no transition and little context, they just happen. Repeatedly. What's most shameful isn't necessarily how bad or annoying these references can be, but that Xebec has apparently decided that comedy isn't even relevant as long as you make piles of references towards shows that the audience may have enjoyed.
There's a point where it becomes funny and then there is a point where it just devolves into frustration and pandering. The occasional anime reference can be quite nice, but in Nyaruko-san it does nothing but infuriate and make watching the series an arduous experience due to their superfluous usage. Haiyore! Nyaruko-san is an anime that has about all the comedic sophistication of Hannah Montana and Meet the Spartans.
For an anime that is constantly parodying other series and their tropes, it really makes you wonder when the same cliches and issues are present in the show itself. Harem members suddenly "transfer" into the same classroom as the protagonist, characters decide to neglect their duties to go on a trip to the beach, the protagonist and main heroine (mistakenly) bodyswap with eachother, and people walk in during inopportune moments and misunderstandings follow as a result. There's a glaring amount of cliches and, sadly, these are mostly important or genuine aspects of the series rather than simple parodies or references. If you're looking for anything unique or original in that regard then you are most definitely not going to find what you want here.
The only thing to set this series apart from any other bad harem anime is the addition of the Cthulhu Mythos, but even this is mostly made irrelevant by how the story and deities are changed and bastardized from their Lovecraftian counterparts. It's an element that seems unique and interesting at the start of the series but it quickly fades from prominence in favor of fanservice and otaku references. A pretty unfortunate fact considering the rich amount of content and depth found in the Mythos. Much more value than in this anime, anyway.
Oddly enough, the series is actually bearable during the rare dramatic moments. When the terrible character dynamic is put aside and Mahiro and Nyaruko think about how much they really like eachother, it can actually be somewhat heartwarming and the characters can almost verge on being likable. It's just unfortunate that these moments can't even be counted with a full hand.
Another minor positive can be attributed to the art. While the budget is modest and the animation quality is passable at best, the vibrant art style and color palette makes the show a lot more pleasing to look at than most. It's refreshing to see something that actually contains color when the majority of anime instead rely on dull hues of grey, brown, or blue. That said, you can polish a piece of trash, but it will always remain nothing more than trash.
It's hard to determine just where this series went wrong. Perhaps the concept of the series was already flawed and doomed to failure, but a large amount of the blame can be shifted towards the studio and their insistence on pandering over quality. For people that are simply looking for a show that they can watch while turning their brains off, this is a poor but not quite terrible choice. For the people who want something more in their entertainment that extends beyond aimless fanservice and otaku exploitation, Haiyore Nyaruko-san is an insulting series with any inherent value or amusing moments being next to nil.
Somehow I think Cthulhu monsters might be less frightening than Haiyore Nyaruko-san.
