The Hour of Twilight was really bad, and these days it would just have been a scenario.
The Well of Eternity was just a movie theater, you didn't really have to do much, everything was just happening for you, and again, could easily have been a scenario.
End Time depended on which rooms you got, happy days if you got Baine, shitty days if you got Jaina or Tyrande.
Zul'Gurub v2.0 was okay, the only boss I really enjoyed was Venoxis, the others were pretty boring.
Zul'Aman was okay, but it felt really odd that an old raid had been degraded to a timed event.
If you compare these to the fantastic Heroics that were introduced at Cataclysm's release it gets rather sad, Stonecore was amazing, Vortex Pinnacle was amazing, BRC was really good, Throne of the Tides was also really good, and the rest went from average to bad, with Halls of Origination being the only bad one at release, where as all the dungeons that were introduced later on in the expansion all go in the bad/mediocre category.
Let's take WotLK too:
Trial of the Champion was extremely forgettable, the mounted combat as always sucked, Eadric was really bland and The Black Knight was a cool concept but wasn't executed very well, only Paletress was good and that's only for nostalgia reasons when she summons visions of the old bosses.
The Forge of Souls starts the trio of the worst dungeons ever in WoW, a 2-boss dungeon who's only memorable thing is the fact that the last boss screams in your face, else it's another dungeon where you could just ignore all mechanics and zerg through it.
Pit of Saron was a joke, every boss was a joke, even Tyrannus was an unintentional joke (at least I presume so) with his stupid "Power OVERWHELMING" line being spammed all the time, and once again all the boss battles sucked except for Ick maybe who had that chase mechanic, which has been done to death now.
And lastly we have Halls of Reflection, which deserves a section for itself since it was so bad. Firstly we have 5 incredibly tedious and boring trash packs, all which has to be done over again if the tank accidentally falls asleep, which I wouldn't blame him for. Queue boring zerg fight #1. Then we get 5 more of the same trash packs, and then we enter boring zerg fight #2. Then.... that happened... I wouldn't even call it a boss fight, because it really just is a gauntlet event, it's like calling the triceratops in one of the Crash Bandicoot 3 stages for a boss, it just isn't, it's a damn gauntlet event, like the Blood Elves in SWP after Brutallus, the little murloc guys in Throne of the Tides before 1st boss and so on. Anyways, Lich King proves once again that he's a fucking idiot when he lets us live and gets crushed by a few boulders, and there goes our oh so mighty expansion villain, beaten by us even before the raid. Without a doubt the worst dungeon ever, and it's incredible how it could actually dissapoint seeing that Wrath had already set the standard incredibly low right from the start.
As you can imagine I was never too keen on these dungeons that were added mid/late-expansion, they weren't fun the first time and certainly wasn't the next 20 times either, and the fact that they replaced great raids like BWD, Firelands, Ulduar and Naxxramas in progression made them even worse. From these experiences I'm ever so grateful that Mists won't suffer from the same disease as Wrath and Cata, which in the end was what limited their content and made me dislike them in the end.
Of course this is all subjective, shouldn't need to be mentioned but someone is gonna call me out on trying to speak of these as facts, when they of course aren't.
And I think since I'm posting in this thread, it's only fair that I also contribute to the actual thread topic, at least just briefly. I think that with 5.2 Mists finally made dailies optional, I don't do them, and I'm doing absolutely fine, experiencing everything I want to. Right now it's very balanced to me, sure we won't get anymore new dungeons, but as you might have figured out by now I'm not weeping over that one bit, it certainly satisfies all of my needs right now, and I can't really see how one would prefer dungeons over raids in any shape or form, but to each his own I guess.