Both works delve into fairly spooky/realistic sides of one’s family.
Both works involve spending time within few specific locations and have a lot of dialogue (though it’s always engaging, intellectual, and witty).
Both works have less then ten characters, but are all a lot of fun and have their own similarities, like how Koyomi and Inumaru are funny male individuals who quite sadly possess an unhealthy definition of love, Tsubasa and Maroko are very cheerful female individuals that cause their own impacts to others around them (espcially towards the male protagonists + they both have their own spooky secrets...), Meme and Muroto are awesome (possibly) middle age men who simply wish to maintain balance within their environment (as well as being intellectual in both a serious and charismatic manner). Everyone else may not share too much close resemblances, yet they still share at maintaining being relevant & enjoyable.
Both works have animal metaphors (Birds in Gosenzo-sama and Cats in Nekomonogatari).
Both works most certainly show that not all stories end with a “Happily Ever After”.