Haiyoru!Nyaruani is an anime with a purpose: To sell the plot of a series of light novels like hotcakes. However, it lacks the bells and whistles to move past this purpose, and ends up drifting into the realm of forgettable. As stated before, this series was made with the intention of promoting the light novel series that it's based off of. As you can imagine, this doesn't leave it very much room to develop, especially with the straining 4 minute length per episode. However, there's enough spontaneity and wackiness to make it a worthwhile, humorous, if unmemorable series to watch. The animation obviously won't bewinning any accolades, due to being entirely done in Flash. While it isn't bad, it's very minimalistic, and doesn't allow for much action to take place. The music and voice work are both satisfactory, if not excellent. From the ominous orchestra in the introduction reminiscent of Dr. Horrible to the emotion-deprived wisp of Cthuko's voice to the upbeat ending, the auditory aspect is easily the high point of the series.

In short, worth checking out, but don't get your hopes up. It may not be amazing, but it did its job well in promoting the story of these books, and I hope that they may get a translation at a later date.
It's split pretty evenly down the line whether fans of the Cthulhu Mythos will find anything to love here, and I'll say that it's an interesting enough take on it to warrant a glance.