I'm at the stage of the game where I'm trying to get keyed to enter the Karazhan 10 man raid dungeon. There has been a long series of accomplishments that led me to the point where I'm at now.
However, to finish my key, I must complete "The Black Morass". Basically you have to protect Medivh while he opens the Dark Portal. It consists of 18 non-stop waves with 3 boss type encounters at waves 6,12, and 18.
I've come to the conclusion that this instance is nothing more than an elaborate gear check. Since completing the instance means you are keyed to enter Kara, the instance checks to see if you are really ready to go.
The entire event is timed. Portals open one after the other and an Elite or Boss must be downed. While the Elite/Boss is up, the portal stays open and adds spawn that go straight for Medivh. Typically a party will have one DPS on the adds and 2 DPS on the boss. This becomes a test of the DPS. Can they do enough DPS to get the Elite and adds down before the next portal opens.
Also, there is some time, at least intially between portal spawns. This is to check your mana regeneration on both your mana based DPS and your healer.
The second boss does a mortal strike debuff on the tank. This debuff will stack up to 10 times and each time it reduces healing by 10% (10 time, 10% = 100% healing reduction = bad) However, the debuff can only land and stack on a normal hit. This is basically a test of your tanks avoidance level. If it's high enough to begin Kara, the debuff won't stack very high and you'll be able to get the boss down.
The third boss does a stun on the entire party (not unlike the one the Tauren in Deadmines does). This gives the 3rd boss a few moments of quality time alone with the tank. The tank is stunned, so he can't dodge, parry, block, anything. The healer is stunned so no healing is done. This is basically just a check of the hit point pool your tank is sporting. If its high enough,he should be able to take a couple hits before everyone recovers from the stun.
So yes, player skill is important, and spec is important, but with Black Morass, you've either got the gear or you don't.
This was really pointed out to me in two runs I made this week. The two runs had the exact same class makeup doing the exact same jobs.
The 1st run we almost made it, and probably would have except that one perons dropped their beacon early on the 2nd boss (recoverable) and we led the boss too far away from the portal, so he reset (not recoverable).
The 2nd run, we barely made it to the first boss, and wiped on him.
The difference was that one of the DPSers was a fresh 70, instead of a player of the same class who had been 70 for a while. and we changed out 1 druid main healer for another. I'm not sure what if any disparity existed in their gear, but everyone seemed skilled and compentent in their jobs.
So basically Black Morass is a gear check. Either your group is geared up enough to do it, or it isn't. This also explains, at least to me, why some people think the instance is 'easy' and others think its 'hard'.