Lasting the length of a single standard episode, Nyanko Days is cute and fluffy, and gets by entirely on being cute and fluffy. In fact, there's so little substance that it's a struggle to even talk about the show beyond its substance.

It's not really that it's bad per se. It's mindless and cute stuff to turn your brain off to for about a half-hour, so it's perfectly serviceable in that regards and serves its function in that way. It's also incredibly cute which no one can deny. It's hard to criticize because it effectively serves its function and arguing against that function just feels like it comes off as weird and nitpicky. But one can afford to be nitpicky over a series that is, effectively, nothing.

When you really get down to it, Nyanko Days is the most anime thing an anime is. Anthropomorphized cats, big eyes and cute faces with characters fitting nicely into archetypes, constant sugary cuteness, loner girl starts to hang out with non-loner girl... it manages to be incredibly exhausting in the very short time it runs, because it feels so much like other similar anime. I don't need originality, but I need something that's derivative with something to offer, and there's nothing here. Not even the cats are cats I can care about. Basically the visual equivalent of "in one ear and out the other".

Part of this is definitely due to the fact that every episode is two minutes long, with only about 70% of it being actual content due to a five-second long opening slate and a 30-second long ED (approximately). There's almost literally no time to even absorb anything is happening, because everything is so rapid-fire that it washes over incredibly easy. Even multi-part episodes suffer from this. It would have honestly been better to split it up into four-minute episodes, or even eight-minute episodes, because at least then you can realize an episode is happening. Even poor slife-of-life anime get by with so-so paced 24-minute episodes; two-minute episodes where a thing happens is beyond the pale.

It does some things serviceable at least, in a way that doesn't make this anime feel like an actual waste of time. Yuuko Konagai and Azumi Shiratori may not be great characters, but they're done fine enough with at least a bit of interest that it's fine (and also have cute interactions together, more cute than anything else in the show). The, uh, arc with Ran Iketani, the girl who's scared of cats, is amusing while it lasts. The ED should be annoying but it ends up being catchy (I still have it stuck in my head even now) and at least has serviceable visuals for it. Aurally, it has a bouncy and bubbly sound design (but especially when the cats are the focus) that it makes up for the lackluster art. Two of the four cats are distinctive. The anime is so short that even if you find it dreadful, you won't have even spent half-an-hour on it. The voice acting was okay.

Really it's hard to name what I like about it when there's so little to care about that I have to stretch myself to name positive aspects. But it's enough to not make it a bad anime, just really mediocre. A lot of it comes down to its awful pacing of two-minute episodes, but even if that were fixed, it'd still be really unmemorable and nothing more than a blip in my memory to remember to possibly check out the manga, if I could ever find the time to do so. So it has some benefits, just not many. If you're that into slice-of-life that you need to watch as much as you can from the genre, or have a spare half-hour you can't spend starting/continuing another anime, then you at least have this. Otherwise, there's too little of value to even passingly recommend. But hey, cats.