It's as much about the content as it is your voice. Many times I hear hosts that think they can just randomly start talking. Sometimes it's difficult to follow as they dart around taking tangents without ever completing a point or thought. They may have a fabulous voice, but what am I gaining by listening? I almost need a whiteboard to draw pictures and take notes to track them.
Other hosts don't even realize how organized their thoughts are and naturally speak in a logical order providing a ton of helpful information, but their speech patterns, ambient noises, poor equipment make it difficult to hear their wisdom and insights.
Both of these issues can be hedged off with a few simple tips.