Let me start with this:
I have been playing Prot Paladin since Burning Crusade. I am familiar with it, and only stepped down from tanking in Dragon Soul because I wasn't raiding much any more. Last night for fun, I got on and tried to do some Firelands (mostly regular) with some friends. It was awful. I have a hard time thinking the healers, who I know, were doing poorly, but I was dropping constantly.
The first thing I noticed was my relic was gone of course, that had my JC gem in it...but that wouldn't explain it, too minute. Then I saw that even with the Mastery buff, I was missing about 28% Chance to block... now, I know that my mitigation works differently now. Actively. But is this why I am so weak? I mean, sure I'll shield slam a lot, always have, but what if I want to WOG? Well then thats 3 holy power not giving me damage reduction? I do not like it at all. I was literally railed by Lava Scions on regular rag. Even during cool downs I was taking major damage.
On top of that, I feel like my threat and damage output is suffering. My DK friend was topping the charts every fight as Blood. I was tickling things. Admittedly, when Alabaster Shield stacks up a few times, and when I put on "Harsh Words", I was able to do a bit more damage, but not much. I will say I love the Consecrate Glyph.
Also WTF they took away Divine Sacrifice and made it magic damage only? This one hurt my soul badly.