Could be a nice concept of a melee warrior with light and dark abilities, depending on the god he prays. The experience I have had with paladins are a religious static warrior with lower mobility than the warrior class, but with some ranged abilities to pull the enemy to himself. I think the paladin should be a warrior with two mana resources (faith and wrath), that way the most destructive abilities use wrath and the most constructive abilities use faith (making the difference between good and evil).
For specializations I think paladin should have a DPS specialization, a tank specialization and a support or buffer specialization.
I think at least one spec should be like wow shaman enhancement combat style. With a vast variety of skills and resources, but to balance his versatility would be great to see him using two types of mana resources.