The following can be a good criteria when evaluating a web directory. Please note this is not the only criteria, you can add more to it if you like.
• Age of directory
• Is the directory indexed
• Is your listing category in the directory indexed
• Number of links to the directory
• Domain age of directory
• Does directory require a link back
• PageRank of directory's home page
• PageRank of the category of your listing in your directory
• Design of directory
• How large is the directory