One of the problems with harem rom-coms these days is the tendency to try and be creative in unusual ways. The problem, specifically, is that the writers and mangaka assume that by simply including something like aliens, youkai, body switching, etc, etc, then the story automatically becomes new and innovative.
Fujiwara Sato, the creator of the manga upon which this anime is based, decided to adds cats. No, not catgirls, just cats (although girls are present in the story as well).
Nyan Koi follows the life of one Kousaka Junpei, a high schooler who lives with his mother, sister, and pet cat, but who suffers from a severe allergy to all things feline. One day he accidentally knocks the head off a statue belonging to the local cat deity, and from then on he can understand everything every cat is saying. His pet Nyamsus tells him that he has been cursed by the cat god, and that unless he helps 100 cats he will be turned into a cat himself.
The only problem though, is that his allergy will kill him at that point.
Now, I will admit to a certain bias here. This past year I have been following two particular manga dealing with cats and humans - Nyan Koi and Koi Neko, and of the two, Koi Neko has the better story. That's not to say that Nyan Koi is bad in terms of it's plot, but it does suffer from a certain genericism brought on by the fact that it's a harem story. That said, the anime adaptation follows the manga pretty well up to the last couple of episodes, at which point it goes off at a tangent.
That's not a bad thing mind, but in the case of Nyan Koi it feels more like an attempt to entice the viewer into watching the second series, especially as, aside from one or two hints, the events in the show don't really support most of the final episode.
However, the plot does have some redeeming qualities in that the humour from the manga has maintained, especially where the cats are concerned. The scripting is also well handled for the most part, barring a few odd inconsistencies come the last few episodes, however this should be no surprise given that much of the show is the anime form of the manga.
The bright and cheery colour scheme reflects the fact that this is a fairly simple harem comedy. The animation is well handled and choregraphed, and the show makes good use of different animation techniques to emphasise the humour. That said, Nyan Koi does suffer from a degree of genericism when it comes to presentation. Certain scenes are reminiscent of many other harem anime, and the characters themselves are formulaic in their designs, and this includes the cats.
In terms of sound the series is well served with it's cast of voice actors, all of whom are very talented in their own right (for example, Tanaka Atsuko, who plays the role of Nyamsus, is also the actress behind Kusanagi Mokoto of GitS: SAC, 2nd Gig, 2.0 and Innocence). The one problem though, is that their talents are underused, however this is purely an outgrowth of the fact that this is a comedy show rather than a serious tale. That said, they do portray their respective characters well, especially in the more humourous moments.
The OP is a simple J-Pop ditty sung by Sakakibara Yui called "Nyanderful" that, while being upbeat, is nothing particularly special. Likewise the ED, "Strawberry ~Amaku Setsunai Namida~" (sung by Imai Asami), while being a more melodic than the OP, is again, nothing to write home about.
In all honesty the music, although being reasonably well composed, is fairly generic throughout the series, and while the choreography is fairly well handled, there is a certain lack in terms of impact because of this.
As far as the characters go, they're all pretty much what one would expect from a harem comedy. That's not to say that they're bad though, as they're nicely presented for the most part. It simply means that they're formulaic and, because of this limitation, they are only allowed to develop in certain ways. However, given the mass of harem comedies appearing over the last few years it has to be said that while Nyan Koi does have generic characters, they're nowhere near as bad as some I could mention.
One thing I will point out though, is that the addition of cats, and their effect on Junpei, is actually beneficial for the series as a whole. While the overall effect isn't really telling to the viewer, the relationship between Junpei and the various felines he helps allows the viewer to relegate the harem aspect of the series, and this allows the humour to come to the fore.
Now I will admit that I did find myself chuckling to this show, as many cat owners might find themselves doing in certain scenes. While I'm not a big fan of harem anime in general, the cats allow one to appreciate the humour in amore defined manner, and the show has less of a need to place the lead male in various ecchi sitautions in an attempt to get some laughs - something which is a big plus in my book.
While the series isn't a complete transposition of the manga, it does have the benefit of allowing the viewer to appreciate the visual humour in a way that the manga just couldn't convey. That said, the last few episodes, being anime originals, do suffer because the writing in them just isn't as good as it is in the rest of the series.
Fans of harem comedies may be of two minds about the show to be honest. There's a number of good points to the series, however there has been no real attempt to step away from the generic nature of the typical harem anime, and this places limitations on what can and can't be done. This is actually one of the reasons why I prefer Koi Neko over Nyan Koi as, while both include cats talking to humans, Koi Neko takes a completely different approach.
Nyan Koi is enjoyable though, and it's the humour that most will appreciate come the end of the series.
It's just a shame that the lesson of Ai Yori Aoshi (i.e. the lead male doesn't have to be generic, mediocre, or a loser), still hasn't been learned.