To define a hypermedia system's ease of use from the user's point of view, we propose three evaluation metrics: an interface shallowness metric, a downward compactness metric, and a downward navigability metric. These express both the cognitive load on users and the structural complexity of the hypermedia contents. We conducted a field study at the National Museum of Ethnology (NME) in Osaka, Japan, to evaluate our hypermedia system and to assess the suitability of our hypermedia metrics from the viewpoint of visiting members of the public. After developing a spreadsheet-type authoring system named HyperEX, we built prototype systems for use by members of the public visiting a special exhibition held at the museum. Questionnaires, interviews, automatic recording of users' navigation operations, and statistical analysis of 449 tested users yielded the following results. First, the suitability of the metrics was found to be satisfactory, indicating that they are useful for developing hypermedia systems. Second, there is a strong relationship between a system's enjoyability and its usability. Transparency and the friendliness of the user interface are the key issues in enjoyability. Finally, the quality of the video strongly affects the overall system evaluation. Video quality is determined by optimum selection of scenes, the length of the video, and appropriate audio-visual expression of the content. This video quality may become the most important issue in developing hypermedia for museum education.