Most people do voice-of-the-customer (VOC) by showing customers the features of the new product they want to make. The customer usually says "sure, it looks fine." There you have it, this describes most "VOC Systems" in action. This is a feature-based approach.
Rather, the best practice is to ask customers what problem they are trying to solve. This leads to understanding their requirements (i.e. needs or customer "wants"). Then we use the information generated from these conversations with customers, called "customer requirements," to define and prioritize product requirements (i.e. product features). The features are HOW we will fulfill the WANTS.
Often this differentiation is confused. People interchange terminology; requirements, features, specifications, needs, product requirements, customer requirements, and so on. Understanding the difference between WANTS (i.e. real customer needs) and HOWS (i.e. the specific way we are going to meet that need with a specific product feature or function) is key to uncovering what the customer values most.
When customers are presented with product features and asked to judge them, outside of the context of their requirements, it can result in a false sense of VOC - at the end of the day we still don't understand the problem they are trying to solve.
Here is an example (from a "green" lighting product) of the difference between a Customer Requirement and a Product Feature...Customers want "controllability" (a requirement) and a way of fulfilling this requirement is through a manual dimming feature, addressable ballast, and/or live load demand response. These are product features. The next question is how much (to what degree) do each of these fulfill the controllability need? This prioritization problem will be the subject of another post.
So what problem is the proposed new product trying to solve? For example "energy savings?" How much of a problem is energy consumption with the current solution? Find the customer needs/wants before you push lots of new features and functionality at them and you will really learn what the customer wants. This is VOC.