This show tends to get compared to Happy Tree Friends, but it comes from a very different place from that.
People tend to label violence and alcoholism and the like as "adult" themes and teenagers particularly will gleefully consume things that are "adult" because it's cool and edgy. This appeal of deviance explains the popularity of "Happy Tree Friends". But that's not what Nekojiru is about.
Childhood is not as sanitary as western media would have you believe. Nekojiru comes from a place that is thoroughly childlike and innocent. Children are morbid and curious, brutal and cruel, innocent and nonjudgmental. Children like to kill bugs, and ask
difficult questions. Children grow up with flawed adults and observe their world without a sense of right or wrong. Nekojiru shows the world unsanitized through the subjective experience of a couple of children. There is no judgment, only brutal observation that happens to be really funny. It shows real things without saying "This is wrong" or "This is right", and the main characters experience it in their raw and childlike (innocently horrible and horribly innocent) way. This sort of matter-of-fact voice is refreshing to me. At times it seems cruel and brutal, but really it's no more cruel and brutal than the reality of things, and, like a child, the show has no qualms about personifying those animals and/or unlucky persons which it later turns out were standing on the wrong side of the food chain and/or society. This curiosity might be called morbid, but on the other hand curiosity is innocent, and it is only from a standpoint of resigned knowledge that personifying a pig that is to be slaughtered might be labeled morbid. Maybe a dash of black humor and a bit of childish exaggeration.
This work probably isn't targeted at children. Like most works worth a damn, it's not targeted at any demographic. All it is, is a real expression of the subjective experience of the world through childrens' eyes. It's really kind of adorable in its childishness, and completely hilarious. All in all, it's more akin to Beavis and Butthead (in its observational humor. particularly in chapter 18) or Calvin and Hobbes (in its freshly subjective child's point of view) than to Happy Tree Friends.
This show also has some really great delivery and overall voice work. It's beautifully blunt and unrefined, fitting its characters.