Originally getting into it from watching anime, I've come to love much of recent Japanese music. In particular, more recently, I've come to enjoy Vocaloid songs. Conversely, my youngest son, who is doing music as a school subject, can't stand Vocaloid.
Now we were talking one day about music and I asked if there were any recent technological developments in music. Then I realised Vocaloid is probably the most significant, even in terms of sheer numbers of songs. Looking scornfully, he said, "Yeah, numbers," as if quantity does not trump quality.
Thinking about it, though, it's unreasonable to say that Vocaloid songs lack quality. Just like any genre or indeed any art form, there will be many pieces that are mundane. That, however, does not prevent a s significant number of pieces that are interesting or thought-provoking or groundbreaking or have something worth appreciating. Human creativity is quite an amazing thing.
Returning to Vocaloid, what is more significant in my mind is that it lets people produce songs exploring a wealth of subjects. For a songwriter without much of a voice, the previous model of finding a vocalist to sing your songs works if it's worth the vocalist's time, i.e., they believe the songs will be financially successful. The advent of Vocaloid sidesteps that need. A songwriter can produce songs without the need of a vocalist, and indeed, without the expectation of financial success. (NB I'm not saying it can't be financially viable, just that it doesn't need to be for good music to be produced.)
That means that a songwriter can produce songs on subjects that are not mainstream, which, to be honest, predominantly seem to be love songs. Of course there are many Vocaloid love songs, many very successful, but it would be interesting to see statistics on the range of themes and subjects explored by songs in both traditional and Vocaloid music, and see if there is any difference. It seems to me that songs sung by Vocaloids cover a broader range of subjects, but it would be nice to have the numbers to confirm or deny that impression.