As the subject expert, you are the person most qualified to judge the quality of an OER. However, there are several criteria that may be helpful in evaluating OER.
The text covers all areas and ideas of the subject appropriately and provides an effective index and/or glossary.
Content is accurate, error-free and unbiased.
Content is up-to-date, but not in a way that will quickly make the text obsolete within a short period of time. The text is written and/or arranged in such a way that necessary updates will be relatively easy and straightforward to implement.
The text is written in lucid, accessible prose, and provides adequate context for any jargon/technical terminology used.
The text is internally consistent in terms of terminology and framework.
The text is easily and readily divisible into smaller reading sections that can be assigned at different points within the course (i.e., enormous blocks of text without subheadings should be avoided). The text should not be overly self-referential, and should be easily reorganized and realigned with various subunits of a course without presenting much disruption to the reader.
The topics in the text are presented in a logical, clear fashion.
The text is free of significant interface issues, including navigation problems, distortion of images/charts, and any other display features that may distract or confuse the reader.
The text contains no grammatical errors.
The text is not culturally insensitive or offensive in any way. It should make use of examples that are inclusive of a variety of races, ethnicities, and backgrounds.