By now, most death knights are intimately familiar with our tier 5 talents, Runic Empowerment, Runic Corruption, and Blood Tap. These can be commonly referred to as our "rune regeneration" talents, which work off runic power abilities to keep runes refreshed at a consistent rate so that we don't find ourselves with over much downtime.
But of course, things weren't always like this. At one point, we had none of these. Our runes regenerated when they regenerated, and if we wanted more runes, all we had was Blood Tap, which at the time was on a cooldown and bought back a single rune with no regard for how much runic power you'd spent. However, back around Cataclysm, Blizzard decided they wanted to shake up predictable rotations, and thus added the rune regeneration as a way to effect that, allowing some variation to the rotation by adding a chance for variable rune regeneration rates.
Unfortunately, this hit its first big roadblock with unholy, which couldn't always properly use the regenerated rune due to its weird rotation, so Unholy Corruption came along especially for unholy death knights, allowing for an easier and smoother regeneration time that allowed them to keep their pace without completely switching up their rotation based on the capriciousness of Runic Empowerment.
When the big patch 5.0 talent revamp came in, we got the infamous tier 5. Not only did every death knight get to choose between Runic Empowerment or Runic Corruption, Blood Tap became its own talent that let you "control" when to get your extra rune. One would think this might be the end of it. You can choose your method of randomness or even go non-random, and all is well.
Still, there's a few problems here. Even with these sorted methods, mathematically, there's probably one that's going to be best for a given spec if used correctly, so there's still a sense, justified or not, that each spec has a "best" tier 5 talent to take. The "rune tetris" issue continues, as people still struggle to line up their runes to get the best runes to regen. There's also the current leveling issue. Since tier 5 doesn't come around until level 75, for 20 levels death knights are stuck with large awkward gaps in their damage rotation as they have no way to regeneration extra runes. In addition, there's the plain old curmudgeonly view to take on it. We didn't have to deal with rune regeneration before, why can't we go back? We'll just get the smooth consistent regeneration we had before and be perfectly happy.
Of course, some death knights argue that having that extra element of unpredictability and a few extra runes offers a good, dynamic change to the class, and so far, Blizzard seems to agree. It may be in 6.0 we'll see some attempts to tighten up the tier and settle the empowerment vs. corruption debate more definitively, but this is one mechanic that is like here to stay, for better or for worse. Rune tetris may just be a part of the class we have to live with.
Plague Leech is a strange talent on the first tier. On one hand, it does exactly what Blizzard says they don't want a talent to do: That is, it provides a noticable, obvious damage boost over the other two option that makes it the clear choice for anyone min-maxing their DPS. On the other hand, very few people bothered to take it because it was just so inconvenient. Many of the most welcome class changes, such as Outbreak or Scarlet Fever, have been dedicated to make it easier to get diseases up and keep them up so that you can get to meat and potatoes of your rotation, the more devastating strikes. Plague Leech changed that by making removing your diseases every 30 seconds or so practically mandatory. Therefore, to use Plague Leech properly, you had to go against your gut and take those diseases down, then reapply them again.
Blizzard finally responded to this in a recent patch not by revamping the talent to make it less of counter-intuitive, but by doubling down and making it regenerate two runes. This improved it to the point that it'd become near-mandatory, with high end min-maxers making stat weight and best in slot lists around the assumption you've taken it.
That said, it hasn't solved either of the two problems above. Plague Leech is now, more than ever, a "mandatory" talent, and it still requires the counter-intuitive move of completely letting your diseases drop. In fact, I'd almost be tempted to call it "clunky."
This, I think, is the issue most likely to see some changes, if only because it does break Blizzard's proclamation that no talent should feel so mandatory. If any of our talents get a major change in patch 6.0, it'll probably be Plague Leech getting replaced or completely redesigned.
Unholy's unholy rotation
Unholy's rotation used to be relatively similar to the other trees. With Scourge Strike a standard frost/unholy rune strike, the arguable major difference between the 3 trees was the color of the buttons you pressed. That's simplifying it a bit, of course, but Blizzard seemed to be constantly toying with Scourge Strike especially. It started completely shadow damage, then went to various ratios of physical-to-shadow damage. Finally, in the great talent revamp that saw blood go to tank only, Scourge Strike went to one rune only. However, that one rune was unholy. While this made thematic sense, it left the unholy rotation in an awkward place by creating "orphaned" blood and frost runes that couldn't be spent except by an awkward use of Icy Touch and Blood Strike. This in itself was solved by the addition of the blood/frost strike Festering Strike. This, however, still left the application of diseases in an awkward place, as using the traditional Plague Strike/Icy Touch method left behind runes that could not be otherwise swept up by Scourge Strike and Festering Strike. This was "solved" by a combination of Outbreak and the addition of a disease refreshing ability added to Festering Strike. This still left the ability to accidentally drop diseases and have an awkward orphaned rune, so they added the ability for Plague Strike to add both diseases. This still left orphaned runes on the AoE rotation, so they added Blood Boil to Reaping.
The end result is that unholy does finally have its own distinct and useful rotation, but a lot of it feels like bandaid fixes (especially for the diseases), and it still leaves the unholy death knight unable to properly use Death Strike as an emergency healing source without tripping up their rotation in a way that frost won't. Leveling unholy death knights have to engage in an awkward Death Strike rotation for a few levels until they finally earn Festering Strike. Frost and blood death knights who want to try unholy have to unlearn habits as they learn to spend runes in a whole different configuration.
So at this point, with unholy, the question is, are we okay with the rotation being so "unique"? Or do we want it to flow better with the other 2 specs and with our normal methods of disease application and AoE? I'm personally in the latter camp, but so far, Blizzard's holding steady. I think the big thing to watch here is whether Blizzard will try to peel off or change some of the bandaids, such as Plague Strike applying both diseases. If they remain, it may be Blizzard has decided unholy's going to be that weird child for a while longer, and it'll just take a bit more work to break into it.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.