It all started with a legendary
If you played a healer during the Wrath era, there was one weapon that you wanted to wield more than any other. Val'anyr, Hammer of Ancient Kings was an amazing legendary weapon for healers, and its power had guilds running Ulduar for years after its release. You could see its defining feature, the shiny bubbles, in every single world-first screenshot. Every healer wanted one, and your power scaled dramatically after obtaining one. With discipline priests highlighting the value of preventive healing, everyone had bubble fever. Val'anyr was invaluable on every single encounter in the expansion.
Discipline priests also had the ability to create heal-based bubbles via their talent Divine Aegis, but the heals had to be critical strikes. In the interest of spreading the bubble love to other classes, Blizzard's developers designed the holy paladin mastery bonus, Illuminated Healing, to mimic Divine Aegis and Val'anyr. The restrictions of requiring a critical strike or a weapon proc were stripped, and all of our healing spells simply generate a bubble that absorbs a portion of the heal's effect.
A holy paladin's best friend
In the Val'anyr days of Wrath, every holy paladin was sporting the Glyph of Holy Light. The glyph caused our HLs to splash nearby targets with extra healing, allowing us to hit several targets at once. Our throughput was second to none, and we were able to dish out our biggest heals without blinking. When Val'anyr's proc occurred, we would simply continue to unload massive Holy Lights on our targets. The cumulative effect of all of those Holy Lights would build up on our target (and nearby raid members), stacking the shield to a very sizable value. The bubbles lasted for 15 seconds and were refreshed with each heal, so you could stack up thousands and thousands of healing points on your target.
The Val'anyr absorption bubbles lasted for 15 seconds, stacked cumulatively, and only required that we use a mace in order to produce them. Holy paladins continued to use Val'anyr right through the Lich King heroic fight, which was considered to be the hardest encounter ever created (at the time). The proc worked simply and effectively, and the cost of using Val'anyr over a higher ilvl weapon was minimal.
What went wrong
When we first received word about our mastery bonus, Illuminated Healing, it looked like Val'anyr reborn. Every single one of our heals would create an absorption bubble, and we could stack mastery on our gear to make them even more powerful. However, even in the first days of receiving the information, many holy paladins were skeptical. The duration of the shields was only 6 seconds, which meant that it would be difficult to keep them up across an entire raid. In addition, the Illuminated Healing effect only started out with a baseline value of 8%, which was only about half of what Val'anyr had been granting us. I hoped that with enough mastery on our gear, we could make up for these deficiencies.
Seven months and several buffs later, our mastery bonus is still unattractive. The baseline bonus was increased to 10% and the scaling per point of mastery improved to 1.25%, but that still wasn't enough for us to hop on board. The duration of the shields was buffed to 8 seconds and is now slated to be set to a Val'anyr-esque 15 seconds in patch 4.1 (currently on the PTR).
Why haven't more paladins started gearing for mastery? It's clear that Blizzard wants us to be using it, as we see it smattered all over our tier set and other plate healing gear. Why is everyone reforging out of any mastery they get? Part of the issue is that much of our healing doesn't even proc Illuminated Healing bubbles, like Beacon of Light and Protector of the Innocent.
Illuminated Healing doesn't stack
The shields aren't cumulative. My World of Logs parses tell me that my average Divine Light heals for about 30k healing. If I had a decent amount of mastery, a Divine Light could leave a 4,500-point absorption bubble on my target. The issue is that if I end up healing someone twice -- say, with two Holy Lights -- they only get a bubble from one of the heals. The Val'anyr bubbles were actually hotfixed to give them a hard cap of 10k absorption per bubble. Even on a good day, my new bubbles will never be half as large as those. In addition, player HP pools have been multiplied several times over in Cataclysm, while the potency of these bubbles remains worse than the original.
When our mastery bonus was unveiled, I predicted that the success or failure of Illuminated Healing hinged on how the bubbles stacked. If they stacked, as Divine Aegis and Val'anyr did, then we would be looking at a very interesting mastery bonus that would create an entirely new branch of paladin healing strategy. We now know that while the absorption bubbles will be generated from the strongest recent heal, they're not designed to stack.
Because the bubbles are only a portion of one heal, he size of our bubbles from Holy Light and Light of Dawn is simply laughable. Even when looking at Divine Light casts, the mastery bubble just doesn't contribute a meaningful amount of throughput for the amount of itemization points we'd have to throw at it. I am glad that Blizzard is increasing the duration of the bubbles to 15 seconds, as that will go a long way toward ensuring their absorption is actually utilized.
The issue with Illuminated Healing is that even when all of the absorption is effective, the amount is still negligible. Stacking bubbles is what caused Val'anyr to be the iconic legendary that we all lusted for, and non-stacking bubbles is what's causing the mass exodus of holy paladins from the mastery stat.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Learn the ropes in Cataclysm 101 for holy paladins, study the new balance between intellect and spirit and learn how to level your new Sunwalker. Tanking is a job, DPS is a craft -- but healing is truly an art.