I believe this to be the best site of its kind. The lessons are easy to understand and are formatted for easy printing. The site is updated regularly and Perry is always trying to make improvements. A number of lessons have been published in book form and can be purchased on the site as well.
Users who sign-up on the mailing list are informed of new additions and changes and are encouraged to review and provide comments on the material.
The amount of information is somewhat overwhelming but it is presented in such a way that users can set their own pace.
I strongly recommend this site to all players.