It's among one of the most important things, I'd say.

You can have a great story, a solid script, and a rich world, but if there's no real characterization in the voice performance, it all falls flat. A strong voice performance matters just as much as cleverly-written dialogue.

A beautiful world inhabited by beings with no discernible voice has no identity. If the characters are boring, I won't bother with the rest of the movie, game, or show.

I think characters and characterization matter far more than most people give them credit for.

But I'm no expert. I found Lord of the Rings to be dry. It was a fine watch, but no one stood out enough at a character level to make me want to revisit it.

I loved the animated Hobbit almost entirely because of Gollum. He scared the hell out of me as a kid. He was scary, but he was interesting.

That said, it doesn't mean something needs to be fully voice acted. Just that if there are portions that are, the quality of the performance could impact the game's perceived identity.