Be sure to consider the following categories while forming your assessment:

Overall Design Quality: Assess the overall design quality in terms of organization and presentation. Are elements appropriately titled or labeled? Is there appropriate spacing, layout, legible type, and other forms of design styling? Is it clear where to begin viewing/interacting with the design? Is the overall display confusing or cluttered? How successful is the prototype in meeting the intended goals?

Visual Encoding: Are expressive and effective visual encodings applied? How well do they reveal the most important features or trends of the underlying data? Is critical data easily seen, or is it unnecessarily "hidden" and only revealed in response to interaction? Are any animations well-designed, including appropriate onsets, timing, and visual complexity? Is the target audience likely to understand the visualization(s)?

Interaction Techniques: Do the supported interaction techniques enable more effective discovery of interesting trends, patterns or outliers? Do they engage the viewer in a process of meaningful exploration or learning? Are the interactions well-implemented, without notable performance issues or usability problems?