Information visualization offers a variety of ways in which digital library collections can be represented on the interface and shown to the user. Metadata, a key component of solid digital libraries, has been utilized to enhance visual user interfaces to digital libraries. This paper reports on a study conducted to investigate and analyze a specific category of digital library visual interface that supports information seeking, exploration and retrieval based on metadata representations, namely metadata-enhanced visual interfaces. This study examined 21 metadata-enhanced digital library visual interfaces from the following perspectives: (a) information access and retrieval features; (b) metadata elements; (c) visualization techniques and metaphors.The results demonstrated that the combined use of visualization techniques and metaphors is becoming increasingly prevalent as a design strategy to support users' information exploration. The results also suggest that visual interfaces enhanced with metadata are becoming more widespread to provide a richer representation of digital collections.