I gave the Warrior Priest in Warhammer Online a whirl. This class is awesome! If the class plays at endgame like it does now, Blizzard is going to lose paladins to WAR. (At least, if there are any old-school hybrid paladins left.)
About a year ago, I posted that the basic nature--the essence--of a paladin was that the paladin heals her allies, and smites her enemies with a giant hammer. Both Retribution and Holy have failed miserably at this.
The warrior priest completely nails this in so many different ways. You need to hit the enemy in order to build up Righteous Fury, which you use to cast your healing spells. So far, my healing spells are a straight HoT, a direct heal + HoT (like Regrowth) and an attack that whales on an enemy and does 250% of the damage as healing to your defensive target.
There's also a lot of smaller touches, like a Righteous Fury-generating attack that does lower damage, but heals your entire party for a little bit. There's an attack which increases the Strength of your defensive target for 20 seconds.
The biggest thing about the Warrior Priest is that you have to attack, indeed you are rewarded for attacking, and attacking does not hurt your healing. Being able to maintain both an offensive and defensive target is what really makes this class work.
The only thing about the warrior priest is that it is definitely a healer, not a tank. It's not really a "knightly" archetype, the way the Warcraft paladin (theoretically) is. It wears medium armor, and is very cleric-like in appearance. I suppose that's irony, that WAR's cleric plays like a knight, while Warcraft's shining knight plays like a cleric.
You can't use shields. And you are expected to heal. But you get to run to the front lines and hit people with a giant hammer. Kind of honestly, that's really all I've ever wanted from my paladin. Though this does mean you get focus-fired a fair amount. As well, juggling both an offensive and defensive target is challenging, as is balancing generating and spending Righteous Fury.
I'm really enjoying playing the warrior priest. Of course, I haven't hit endgame, I'm only Rank 9 (of 40), and we did not see the over-specialization of the paladin until the endgame in WoW. But still, I have to give kudos to Mythic for designing an amazingly fun melee-healer.
(If you play Destruction, the equivalent class is the Disciple of Khaine, with similar mechanics. But evil elves are so 1990s. Plus, as Order you get instant scenario queues!)