potentially 🌶️ opinion:

a lot of vocaloid songs are kind of a flop in my eyes, because the best ones are songs that are aware that - while technically impressive - vocaloid singing still exists in uncanny valley

the best songs often work with this and lean into more of an electronica vibe, or are built around lyrics/a mood that is enhanced by this uncanny quality (like Meltdown, which is really grim lyrics-wise and exists as an exercise in the junction between lyrical meaning and upbeat song)