It occured to me that someone who reads back on what I've written over the past month might get the impression that I'm a Pally Propoganda Artist, and am campaigning for the ethical treatment of Retribution Paladins worldwide. In some cases I am - however, I can acknowledge our shortcomings and faults. I've hinted at or lamented some of the negatives tied to playing a Retribution Paladin, but here's my attempt at compiling them in one place.
Retribution Paladins are sub-optimal for 5-man content. In instances where there are groups of 5-6 enemy targets that need to be accounted for, every form of crowd control is needed unless you have a Protection Paladin and outgear the content. Heroic Magister's Terrace comes to mind - there are frequent pulls of 4-6 Blood Elves, and the damage they can dish out is hard to heal through, even with a tier 6 tank and healer. Repentance and Hammer of Justice simply do not compare to Polymorph, Sap/Blind/Stunlock, Hunter traps, or even Fear. I know this problem is not unique to Ret Paladins, but that does not disqualify it as a problem to be addressed. In addition, the mana factor weighs heavily in 5-mans, as Retribution Paladins don't achieve any semblance of mana efficiency until they have full 25-man raid buffs (3-4 blessings, Mana Spring Totem, Windfury Totem, Judgement of Wisdom).
Ret Paladins are behind the curve in 10-man content. They do not bring a dependable, renewable crowd control that is applicable in most instances, nor do they operate with any efficiency without full raid buffs & Judgements. Oftentimes there is only 1 of each class in a 10-man, so the maximum a Ret Paladin can expect as far as buffs to help mana efficiency is Judgement of Wisdom (applied by the Ret Paladin) and maybe a Mana Spring & Windfury Totem, if that. Blessing of Wisdom is last on the list of desirables (Salvation, then Might & Kings first), and there are no guarentees that there will be a Shaman in the raid, nor that the Shaman will be in the Ret Paladin's group to give him his precious totems. The only thing that can be depended on is that Judgement of Wisdom will most likely be up on bosses, even though it will cost the Paladin his Judgement of the Crusader.
On raid utility...
Ret Paladins are the only raid role that relies on other raid members to actively participate in his raid utility. A single Fire Mage can keep Scorch and Fire Vulnerability up by himself; a single Warrior can apply Demo Shout, Sunder Armor x5, and Thunderclap to a mob; a single Feral Druid can apply Faerie Fire and Mangle to a mob. However, a single Paladin cannot apply all the necessary Judgements. Two Paladins (at least) are needed to apply JotC and JoW, or else the raid needs to choose which one is more important. And thus, a semblance of utility is lost.
All that said, groups are not one-role-fits-all. Ret Paladins are a tough puzzle piece to work with. They are not well-rounded and polished and cannot fit into just any puzzle - if you try to jam one into a group, you'll find the group is a bit unwieldy and doesn't give you the results you want. If you surround a Ret Paladin with complementary pieces, however, and place it into a large puzzle, you get a sum that is greater than its parts and the Ret Paladin piece can become a cornerstone.
Bah, there I go again with the preachy proganda. I swear, sometimes I can't help it. Anyway, what I'm trying to say is that Retribution Paladins have their flaws, and just because I enjoy playing one and think they have a ton of tools in their utility belt doesn't mean that everyone should be looking to grab one for every group they form. They have very glaring drawbacks (especially in small groups), and are almost never the best choice for the core of a group. They are more of a luxury item - one you can purchase and use if you have room and resources available. They pay great dividends, but not everyone can afford to get one. If I were creating a group to run a 5-man and could pick any class combination, a Ret Paladin would most likely not be involved. But, as with many things in Warcraft, there's more than one way to achieve a goal, and if your goal is running a 5-man instance and you're not trying to min/max your group for absolute maximum potential effectiveness, you won't be gimping the group unnecessarily in many cases.
All in all, just promise me one thing - if you're creating a 5-man and a Ret Paladin offers to come, you don't turn him away just to keep spamming trade chat with "LF1M DPS for heroic PST!"
EDIT: Blog cruisin', as usual, I ran across a recent post by Aurik about 5-man group balance. It's a good read, and related to some of my recent posts.