I've listened to quite a few Vocaloids, probably, I just haven't recognized them. And stories? That's the tip of the iceberg. Music isn't just about stories. It's the spontaneous expression of ideas. That's how I feel it is, anyways. Music is letting your interior emotions go, transcribing them into song. Raw emotions. I should know this, being a jazz player and also a composer.
And emotional songs, huh? How about Big Bang, I dunno. I don't like emotional songs, but there's a lot of Korean songs out there that really pull at your heartstrings. They focus on things from love to love gone to heartbreak to a lot of things in life.
Well, we're human. But there's a reason why artists typically focus on one genre and mood, it's because they want to sing songs that feel that way. What's the point of doing something if you don't enjoy it? I mean, except for money, but seriously?
Artificial voices never will match a real human's voice. That's just my opinion though. "I for one welcome our new computer overlords", lol. But anyways...
And to conclude, here's a song by SOUND HOLIC that I personally enjoy. You'll likely enjoy it as well. There really isn't a coherent theme, is there? But there's an overall mood present, and that's what matters.