All three Paladin specs are undergoing some pretty significant changes, but as I've historically avoided Holy like the plague (granted, that's based on a Vanilla/BC era issue where non-Holy Paladins were mocked as "doing it wrong," which hasn't been an issue since Wrath) I can't comment so much on that.
This might not go into FinalBoss.tv levels of depth, but now that I've had a good amount of time to play on the PTR, I'm getting a real sense of how these specs work.
The removal of Holy Power from Protection means that you're going to need to be a little more careful using your Shield of the Righteous. The ability now has three charges, and Judgment will now speed up its recovery time by a second or two if it crits. It hits pretty hard and of course gives you your main defensive buff, so you'll still want haste to increase its recovery speed and allow you to Judge more often, but the value of crit also goes up a bit thanks to Judgment.
Consecration on its own is still just an AoE damage ability (and sadly, the super-useful Glyph of the Consecrator is gone, so you'll need to be aware of where you're placing it.) However, many of your abilities now get buffed when you're standing within your Consecration, including Shield of the Righteous, which means it's a very high priority to make sure that this thing is down at all times. Thankfully, its duration no longer goes down with your haste, so as you stack haste, you'll get a grace period between when it goes off its cooldown and when your previous Consecration expires.
Hammer of the Righteous fully replaces Crusader Strike for us, but now it only does its AoE damage when you're in your Consecration. That said, there is a talent row that either gives all the Consecration-enhanced abilities their Consecration buffs at all time (and removes HotR's cooldown entirely) or another that replaces the ability with an always-AoE ability, so you really have to kind of opt in to this restriction unless you're below level 30.
Light of the Protector is the replacement for Word of Glory, but it's way less powerful, as it now only heals you for a portion of your missing health. So there's not much reason to use this when you're at 90% or even 75%. It is, however, a pretty nice emergency heal on a generously short cooldown, but currently it's not really working (hopefully fixed by the time the expansion goes live!) So don't expect a reliable almost Lay-on-Hands level heal from this.
Prot does lose a few abilities, like Holy Wrath and Hammer of Wrath, but with talents you should be able to replace Holy Wrath's snap AoE with things like Hammer of the Righteous.
The key to Prot I think is going to be proper placement of Consecration and judicious use of Shield of the Righteous. I haven't run a dungeon with it yet, but it seems perfectly functional.
While Ret is keeping Holy Power as a resource, the spec feels very different. You'll need to do a bit more planning with it and get used to a kind of ebb and flow to its damage.
The biggest change is Judgment and the new Mastery. Judgment no longer generates Holy Power. Instead, Judgment now buffs all Holy Power consumers on the target, with the buff increased by your Mastery. Judgment also chains to other targets, so you won't be totally screwed in AoE situations (that said, Ret's definitely not as super-AoE-y as it has been.)
The Judgment window will remain the same duration regardless of your stats, so as your gear improves, haste will allow you to keep the debuff on your targets up for more time, which might make the rotation simpler to pull off.
A few abilities are gone, like Exorcism and Hammer of Wrath. The big replacement is Blade of Justice, which hits pretty hard and generates two Holy Power. Also, Crusader Strike has, I believe, two charges baseline.
The flexibility in the rotation will help a bit in making sure that you have enough Holy Power to use your Judgment window effectively. My Paladin has about item level 710 at level 100 (both in Ret and Prot - a lot of it's the same gear) and I was able to get three or sometimes four finishers off within the window.
I think the real key is that Ret is going to be less about hitting whatever ability is available at the time and a bit more about planning ahead. You don't want to spend your Holy Power as soon as you can, and while I'm not sure what the perfect rotational execution would be, you might want to save Judgment until you have the full five Holy Power to fully take advantage of it.
Another really interesting quirk to Retribution is that it's basically the only spec that still has longterm buffs. You have a total of three Greater Blessings you can give out - any mix of three including Might, Wisdom, and Kings. Might now gives a chance to deal additional Holy damage on the target's attacks. Wisdom regenerates health and mana, and Kings periodically adds a damage absorption shield to the target.
These Greater Blessings can only be applied outside of combat, but they will persist through death. While soloing, you'll just put all three on yourself. I'm not sure if you can only do one of each, but if not depending on the content you might spread Might blessings to DPS or if you're having a harder time with survival, you could toss Kings on a tank and Wisdom on a healer.
Of course, with all specs, getting your artifact weapon will add a new ability and modify a lot of the existing ones. For instance, Ret's Ashbringer will grant Wake of Ashes, which is an AoE attack that eventually generates a full five Holy Power on use, which will probably really help getting more finishers into the Judgment window. But this is what you'll get when you log onto the game after 7.0 drops.