Great for kids, positive messages
First off, the very concept of Vocaloid culture... All of the songs in this game were made by fans, not by Sega. With Vocaloid, anyone can contribute to the fandom by writing songs or drawing fanart, or covering songs themselves, and no interpretation is wrong. This game includes a lot of kid-friendly Miku hits in various genres made by people of all sorts of backgrounds. The Hatsune Miku concerts all feature songs made by fans, and there are even unofficial fanmade concerts. Anyone can contribute and encourages artists and musicians to interpret Miku and friends however they want. Even Americans can contribute to the culture, as English versions of Miku exist as well as English Vocaloids like Oliver and Avanna. With the simple tools in this game, this could be a great first step into Vocaloid culture.
A lot of the songs in this game have very positive messages, or thought-provoking stories that can be discussed with parents, but unfortunately Sega didn't include English subtitles so they are lost on people who don't speak Japanese, unless they look up subtitles on YouTube. Piano Girl, YumeYume, and Do Re Mi Rondo are very uplifting, and Story of Evil (aku no musume and Aku no Meshitsukai) is a rather complex, thematically heavy story. There are a lot of other songs with positive messages or good stories, like Kokoro (the first Vocaloid song to ever make me cry, way back when I was a tween) and Hello*Planet.
The creative tools provided with the game are very easy to use and great for kids, especially because actual Vocaloid software is expensive and needs a lot of learning to use efficiently.
There's very little objectionable content compared to Project Diva, the worst that happens is an implied beheading (the sound of a guillotine and a ribbon dropping to the ground) in Story of Evil, some modestly suggestive (Japanese) lyrics in Romeo and Cinderella and On the Rocks, as well as alcohol reference in Clover Club.
As mentioned in the main review, there's not much depth. More experienced players may be turned away by the more easy difficulty of the rhythm game (but some songs like Matryoshka provide a good challenge), and the My Room mode has very few things to do compared to games like Animal Crossing, Tomodachi Life or even the Diva Room in Project Diva.
Very great for younger Miku fans (and older ones who aren't too good at rhythm games or will play anything with Miku in it), fans of nendoroid figures, and young girls who are into anime (who will inevitably happen to be Miku fans).