I've been messing around with patch 3.3 a bit lately, and while there is some interesting lore, and some fun scripted dungeon events, after playing through them all once I've noticed one glaring problem.
It's way too easy.
I'm not even talking about my own personal definition of easy which probably differs from the norm, but about the fact that I can join an entirely random group of players from completely seperate realms with the new PUG dungeon tool and still run downhill through an instance and not only complete it flawlessly but get some of the "achievements" without even trying makes no sense at all.
The whole point of heroic dungons in the first place was to give people something challenging to do outside of raids, but instead of creating another tier of difficulty in heroics they have simply made heroics normal, and normal easy. We're still lacking an actual hard mode for five man instances.
Ideally they would make heroic instances actually challenging even for end game players but as I don't see that happening I have another suggestion.
I'm sure many people wont like the idea, but I propose the permadeath difficulty setting for 5 man dungeons, or even 10 and 25 if you're feeling particularely bold.
It wouldn't simply be if you die, you're gone, but if your entire party wiped... you would be done. No more characters, and instead of simply increasing the quality of loot slightly from each boss or giving you items that, with WoW's ridiculous itemlevel system you would end up replacing in three months, you could gain permanent stat increases, or even an extra talent point? Maybe unbalancing, but it would have to be a reward that truly lasted as otherwise it just wouldn't be worthwhile.
If they wanted to really make things interesting.. release a new dungeon that can only be completed once across all realms, and only on the permadeath setting. The question at that point wouldn't be whether or not WoW has challenging content, but if their web servers can handle the torrential downpour of tear-filled posts.