While I did enjoy the story (the narrative) itself, I did not find the accompanying illustrations of Wanda Gág's Millions of Cats all that visually appealing. I have never really liked black and white illustrations all that much, and the many, many cats together kind of remind me of masses of lemmings, rodents or locusts, faceless swarms of animals with no personalities or individual features (the only personable cat, in my opinion, is the little kitten left at the end, all the others are just a big mass of "catdom").
Now after having read some of the more negative and critical reviews from GR friends regarding Millions of Cats, I was actually at first rather reluctant to read it, as I assumed that it would describe in detail the cats eating each other and fighting amongst themselves. However, as others have indeed previously stated, the violence (or rather, the implied and supposed violence, as we only have the assumption of the old couple that the cats might have eaten each other) happens off-screen and thus is not ever really visible or even described. And furthermore, because there is an element of disbelief present (the old man brings home not just too many cats, but millions of them) this probably renders the author's, Wanda Gág's presented text much less problematic for children, who often seem able to accept the often grotesque violence in fairy and folk tales, simply because it is unbelievable, or just too overly exaggerated.
For me, Millions of Cats is not only an entertaining and intriguing story (albeit one with illustrations that I personally do not find all that aesthetically attractive), but also presents a cautionary tale about human responsibility, or more to the point, the lack of human responsibility. It was the old man's responsibility to find one cat to bring home, but he brought home millions. And later, when it becomes obvious that there are simply too many cats, the old couple again does not face their responsibility or accountability; they simply force the cats to fight it out amongst themselves. Furthermore, the fact that the original hill the old man sees is literally covered with domestic feral cats might also be seen as a lack of pan-human responsibility to both domesticated animals (including pets) and the environment in general (humans abandoning domestic cats in the wild and not realising or caring that there are likely not enough natural spaces available for all of them, that the feral cats will also need to eat and drink, and that the cats' presence will obviously also affect the environment, their surroundings). I know that many people regard Millions of Cats as an allegory against vanity, but I think that it could and really should also be interpreted as an allegory against irresponsibility (and perhaps even with more justification than this story being a cautionary tale against vanity). You might even say that Wanda Gág's Milliosn of Cats could easily present one of the first picture books (one of the first books for younger children) to somewhat promote environmental responsibility, by showing that we cannot simply allow domestic animals to overrun nature.