This is an experiment.
One of the things that has confused me a little are all of the posts from players who say they don't understand the role of the priest class. It is unclear to us why there is so much confusion about this particular class, which seems to us to be fairly straightforward.
We are often reluctant to lay out our design goals very clearly, because frankly some players tend to use those statements to attempt to lawyer us into changes ("I'm supposed to be the master of AE damage") or would rather argue about the design instead of providing feedback on how the class actually works.
Nevertheless, because players have asked for it so often and in the interest of trying to foster the discussion, here is what we think of as the role of the priest class.
The Role of the Priest
The priest is a caster class that uses Holy and Shadow magic. Priests can only wear cloth armor and have a limited selection of weapons, but do most of their damage and healing from range. They make up for their low armor with spells that offer protection and healing.
Discipline -- this is a healing tree that emphasizes survival and single-target healing. Discipline specializes in damage absorption and prevention rather than restoring health, although they are very capable in that department too.
Holy -- this is a healing tree that has a spell suited for every situation. Holy priests can heal groups, heal individuals, heal tanks, or do all three in a single encounter. They are better at group healing than Discipline priests, but don't have as many damage prevention capabilities.
Shadow -- this tree sacrifices healing for damage. Shadow priests can restore health and mana to their group while casting their spells. Like the Shadow damage of warlocks, Shadow priest damage tends towards drains and damage over time spells.