And Taepsilum talks about that too. He says that "we're not actually planning in making them as hard as the hardest heroics of all time, like the hardest from TBC, or GB and Stonecore from Cata", which will no doubt ease your worried minds, although personally I really liked that you had to work hard to get through the Cataclysm heroics. They didn't seem too hard, just hard enough that you had to know how to play your class, know the encounter, and have decent group DPS to get to the end.
Getting the difficulty right
Taepsilum clarifies that the target difficulty for Heroics will be around Heroic Vortex Pinnacle. And that's about perfect in my book, maybe leaning towards the easy end. Let's think through Vortex Pinnacle and what it entailed, particularly early on in the expansion. The first pull of five elementals was your early test of your group. If you had a shaman on board, or a pally with glyphed Holy Wrath, you were usually OK, but other than that, you could have a hard time with these and the other elemental mobs in the zone. Boss number one was one that could certainly wipe your group, the lightning crackles that came out from the drawn-in tornado shield could do some damage if your healer wasn't on the ball, and nobody was using personal cooldowns.
The second boss, Altarius, was a fun fest. Tornadoes that knocked you into the air, and the mechanic of being upwind or downwind of the boss as well as a painful chilling breath were fun to handle, if occasionally frustrating thanks to tornadoes chaining you into the air multiple times. Nothing too tricky, so long as your reflexes and your graphics setting were about right.
The last boss was great, in my opinion. As long as you could time a jump perfectly to not get hit by his Static Cling ability, he was the easiest boss in the instance. Yes, healers could dispel it, but often not fast enough to save everyone. With Mists abilities like Windwalk Totem, it would be trivial, but so many groups fell foul of the simple "hey, jump" mechanic. As a paladin, you were away, thanks to Hand of Freedom, and Priests could Mass Dispel, and there were several other outs, but it was a really simple mechanic that resulted in a swift demise if you couldn't deal with it more than a couple of times.
None of these bosses had any real one-shot mechanics, like Ozruk in Stonecore, whose ground slam and shatter would both likely take you out, especially at lower gear levels. This is key: being one-shotted is very frustrating, and second chances to learn and get it right the next time are a key part of not becoming angry. You can't heal through a one-shot mechanic, and yes, all you had to do was run away from each of them and ensure that he was tanked into a wall, but it was still annoying when you got it wrong, and something a lot of groups struggled with. Vortex Pinnacle lacked any of these.
And Taepsilum has it right again when he says that the visual clues on highly dangerous mechanics need to be super-clear. Shatter famously extended slightly further than its bubble, which was hard enough to see in the first place. Once you knew, it was fine, but visual AoE effects that match the damage areas are key to making hard mechanics less frustrating.
What's more, random elements are immensely frustrating. I touched on one earlier with Altarius' cyclones that throw you into the air, the randomness that could lead to you being bounced from one to another was annoying. Why is randomness so troublesome in encounters? Because it is something that you can't work around. You might just have to get lucky. So random effects, in order to avoid frustration, need to be at least relatively mild.
What's the big deal with frustration? Why are we talking about that? Well it's why people ragequit. They feel like they are doing their best, and still getting nowhere. It's frustrating. And even the easiest of heroics can cause it. While some frustration is OK, things like non-obvious one-shots and random elements that wipe you can get really tiresome. So managing player frustration to minimize rage-quits is of paramount importance for the success of these heroics.
What about Challenge Modes?
"But Olivia, there is challenging 5-man content in Mists!" This has been a pet hate of mine since it was announced that the first set of Mists 5-mans would be the last. Challenge modes, while great content for a specific type of player, are not the same as heroic 5-mans. Firstly, their reward structure is different, although both drop valor and gear. But the big difference is the group -- friends versus strangers. For me at least, part of the fun of heroic 5-mans was taking a group of strangers and all working together to achieve something tricky.
When 5-man content is hard, you get fewer unpleasant people. When you have to cooperate to get anywhere, you do. This, in my opinion is one of the big problems WoW is facing at the moment -- the absence of difficult randomly matched content. If you don't really know how to play your class, you can disappear into anonymity in LFR, or you might slow down a 5-man if you find yourself in one. Chances are the other players in your group will gather up the slack.
Imagine that happening in Grim Batol, where you knew that if you didn't have a certain level of DPS, the final boss, Erudax, simply wouldn't die because the adds wouldn't be taken down fast enough. You had to work together. And when it worked you felt like you'd achieved something. That feeling built community, it developed respect. Even if you never saw those people again you learned how to work with others because if you didn't you failed. That is all but gone in Mists.
And all this is why I'm so incredibly excited about Taepsilum's post. I really hope this comes to pass, it's a fantastic change, and that these hard 5-man heroics keep on coming right through the expansion. I'm excited.