The three rogue specs share many common mechanics. They all follow the same formula: generate combo points, use finishers, activate your cooldowns when they come up. The real differences between the specs only show up once you start playing them. Assassination is well-known for being more relaxed and favors pooling energy over spamming attacks. Subtlety rogues have a knack for massive burst damage via their complex cooldown, Shadow Dance.
Combat is arguably the simplest of the three specs, and is often characterized by its fast-paced gameplay and high actions-per-minute rate. Adrenaline Rush, which has been combat's signature cooldown for years, is designed to let you push buttons even faster. Assassination's Vendetta lets you hit harder, subtlety's Shadow Dance lets you use openers, and Adrenaline Rush doubles the numbers of buttons you can push. Unfortunately for combat, the concept of "push more buttons" can't scale forever.
The 1-second GCD
The GCD, or global cooldown, has multiple purposes. By invoking a minimum amount of time between abilities, Blizzard can reduce the amount of burst damage that classes can do. It ensures that the server has time to process each ability and action, so that spells don't occur out of order. Imagine if a mage could unload his entire mana pool into a barrage of hundreds of Ice Lances at once. It wouldn't be very fair for anyone else. A rogue dropping multiple Ambushes at the same time would be similarly overpowered.
Rogues have always had a short GCD. Even in vanilla WoW, we had a 1-second GCD that let us make split-second decisions and unload multiple attacks in short time windows. The default GCD is 1.5 seconds for most other classes, which made playing a rogue feel slightly faster and slightly more fluid. I was personally drawn to the rogue due to the quicker gameplay and the ability to react quickly to my enemies.
When 1-second isn't enough
A rogue's base energy regeneration rate is 10 energy per second. With a 1-second GCD, we could use a move that costs 10 energy every GCD. We don't have any DPS abilities that cost 10 energy, so we're obviously not using every GCD available to us all the time. Haste rating on our gear, buffs in our groups, and Bloodlust during burn phases can all increase our energy regeneration. There are also several spec abilities that grant bonus energy or increase our energy regeneration rate. All of those pale in comparison to Adrenaline Rush.
Adrenaline Rush doubles our energy regeneration while active. If we were pushing buttons every 4 seconds before, we're pushing them every 2 seconds during Adrenaline Rush. As we obtain more and more haste, we're able to use more and more abilities. Luckily for us, we've never quite reached the threshold of being able to use an ability every 2 seconds, so we've never been truly GCD-blocked during Adrenaline Rush outside of Bloodlust situations.
Shadow Blades and the 4-piece tier 15 bonus
The new 4-piece bonus on our tier 15 set cuts the energy cost of our abilities by 40% while Shadow Blades is active. If we have the set bonus, we can use 40% more abilities per second, or cuts the time between our abilities by 40%. Suddenly, we've moved from using an ability every 3 seconds to using an ability every 1.8 seconds. Shadow Blades also penetrates our target's armor and grants us double combo points, which means we want to pair it with Adrenaline Rush to achieve the maximum effect. The problem is that AR's energy-doubling effect would have us gaining enough energy to use an ability every 0.9 seconds, which is shorter than the GCD. What now?
Blizzard decided to allow the set bonus to drop our GCD by a few fractions of a second. There is already a Glyph of Adrenaline Rush that does the same thing, and yes, they stack. The goal was to lower the GCD enough to allow rogues to use their abilities as fast as the energy came in. Now, during SB+AR windows, our abilities have less than a second delay before the next one is ready to use. We're finding ourselves pushing Sinister Strike and Eviscerate as fast as we possibly can.
Latency doesn't like short GCDs
One of the biggest problem with enforcing a short GCD is latency. If you're playing with an average ping time of 100ms, it could be 0.25s before your Sinister Strike press leaves your computer, is processed by Blizzard's server, and then confirmed back to you. You won't know how many combo points your SS generated until you have less than half a second before your next move needs to be determined and then pressed. Who has reaction times that good?
If you're playing in a situation with high latency, like on wireless, your ping times could easily exceed 200ms. Now you're left blindly spamming Sinister Strike and hoping that you push Eviscerate at the right times. Blizzard's servers also had issues handling the low GCD times, as they're forced to process our incoming abilities faster and faster. Ghostcrawler confirmed that while lowering the GCD time might have fixed the energy capping problem in this tier, it also isn't a perfect solution.
What's next for combat?
When combat's whole niche is "push more buttons" it can be hard to figure out where to go from here. You can only push so many buttons so fast, and combat with the 4-piece bonus definitely pushed that envelope. In order for combat to continue to scale in the future, I think the 1-second GCD needs to be respected and other ways to boost combat's damage should be evaluated. The issue is that assassination and subtlety rogues are both nowhere near being GCD-limited, due to the high energy cost of their abilities and their lack of Adrenaline Rush.
How do you solve energy capping, then? I'm not sure. There's a lot at play with Adrenaline Rush, and most of the solutions feel very messy. Extending our max energy pool during Adrenaline Rush doesn't solve the problem, making our abilities cost twice as much but deal double damage is redundant, and inventing a new high-energy cost ability to use during AR is just making it Shadow Dance. The goal of Adrenaline Rush is to provide the rogue with a lot of fun, active damage. Teasing around the 1-second GCD is what we want to see happen. So how do you ensure that your energy regeneration never teeters into the sub-second-per-ability range? We'll have to wait and see.
Sneak in every Wednesday for our patch 5.2 guide, a deep-dive into the world of assassination and combat rogue AoE rotations -- and of course, all the basics in our guide to a raid-ready rogue.