Back when The Burning Crusade launched I can remember trying the new 'heroic' dungeon mode out. We went in with a couple people at less than max level and got absolutely butchered. Most of the trash had cleaves which hit our melee for more than half their max health. Byung and Tom died on pretty much every pull. We did manage to get one boss down before figuring we should actually get everyone to max level and get some gear before trying again. Some of the BC heroics were truly brutal and were very hard even with awesome gear.
Wrath of the Lich King heroics were locked so you need max level to even try them. They were easier than TBC heroics were at launch but they were still pretty tricky. We died some but I don't remember ever giving up on one of them. They were all doable at max level with reasonable gear.
Cataclysm went way back in the other direction. I can remember giving up on heroic stonecore in the early days of the expansion. The problem here was with healer mana. They'd gone to a new system and healers simply needed a higher gear level to succeed than in Wrath. I'd like to think our healers played quite well and we likely won more than an average group would have but in some cases it was flat out impossible at low gear levels.
Cataclysm may have been a tad too difficult but I actually liked it. Having a chance for failure makes things interesting. It would be better if the chance for failure was skill related but having the outcome be up in the air makes things a little more interesting. Yesterday Tom and I did some Mists of Pandaria heroics and there was no chance for failure. We did 6 heroics and I didn't die a single time. That's unheard of when compared to heroics from previous expansions. Even Wrath had some deaths! To make things even worse we actually pulled the final boss of one of the dungeons with our tank (Tom) dead. No problem. The hunter switched to his turtle pet and we 4-manned the final boss. Of a heroic dungeon. While we were still wearing a lot of leveling greens.
That just shouldn't happen! I want to die! On another boss I didn't understand the mechanics and actually just stood still while trying to read tooltips for most of the fight. Didn't matter. You can easily win down a DPSer.
Now, they did add a difficulty above heroic this time around so maybe they made heroics particularly easy with the thought that people like me who want to lose can go lose in challenge dungeons. Unfortunately i can't play in challenge dungeons right now because there is no 'looking for challenge mode' tool. Tom and I can't just play with random idiots. We need to co-ordinate with 3 other people like back in the old days. In a week or two when Brendan, Pounder, and Sky hit max level this will become an option but for now we're kinda stuck if we want something hard to do. Maybe it would be worth trolling trade chat/the realm forums to find 3 other people that way?