Lead Systems Designer Greg "Ghostcrawler" Street posted an entry on his blog yesterday called "Wow, Dungeons are Hard!" It's a rather lengthy (but worthwhile) read about the current state of Cataclysm heroics, Blizzard's philosophy on designing them, his impressions on their current difficulty level, and some advice for improving your performance.
Like I said, it's an epic post, and we won't reprint the whole thing here. This, however, is the key takeaway:
On the other hand, we don't want you to stumble your way to victory. We don't want you to be able to overwhelm bosses without noticing or caring what they're doing. We don't want healers to be able to make up for all of the mistakes on the part of the other players. While at the end of the day, dungeons may just be gussied up loot vending machines, we want you to do more than push a button to get the loot.
Ultimately, we don't want to give undergeared or unorganized groups a near guaranteed chance of success, because then the content will feel absolutely trivial for players in appropriate gear who communicate, cooperate, and strategize.
All that being said, though, is Blizzard really satisfied with its dungeon designs and their current level of difficulty? Hard heroics are indeed hard, but the updated PTR patch notes for 4.0.6 (which went live just yesterday at almost the exact same time Ghostcrawler was discussing heroics) indicate that a series of nerfs is coming our way. That will no doubt lead to player rejoicing, but remember -- heroics are naturally getting easier as people get more familiar with them and players continue to compile better gear, which makes completion even easier still.
When patch 4.0.6 goes live (presumably in a couple of weeks), Baron Ashbury will no longer cast Mend Rotten Flesh. Beauty will lose one of her puppies, the poor thing. Every single boss fight in the Stonecore (IMO, the most dreaded of all the heroics) will be nerfed -- Corborus will jump less, High Priestess Azil's adds will die more easily, and Slabhide will drop fewer rocks upon your collective heads. Admittedly, some of these fights were clearly in need of a fix -- Ashbury is a nightmare with some group compositions. Still, it's an interesting mixed message: "Heroics are supposed to be hard, but in patch 4.0.6, we're making them significantly easier."
World of Warcraft: Cataclysm has destroyed Azeroth as we know it; nothing is the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion, from leveling up a new goblin or worgen to breaking news and strategies on endgame play.