Comparing heroics in TBC with heroics in Wrath is like comparing an archbishop with an archmage: they may have the same prefix, but they are nothing alike.
TBC
Heroics lived up to the name and the hype surrounding this new concept. Blizzard wanted to introduce real hardmode versions for level capped players. Heroic modes that really challenged players to be well-geared, well-versed in the fights, and situationally aware. They were like mini-raids and required knowing every encounter, being quick on the CC, utilising all of your buttons and cooldowns, and having a decent collection of gear from end-game normals and professions.
Wrath
"Heroic" dungeons simply bear the name. They are the level 80 version of lower level dungeons. The "end-game" dungeons were only level 78, and so taking a different approach while maintaining the same description was Blizzard's way of giving us more content. If you don't know every aspect of every boss fight, then the penalty is never overwhelming. Until the ICC-5 dungeons and their heroic modes were released, we didn't really get a taste of any sort of challenge. And when we compare even those with Magister's Terrace, or places like Shadow Labyrinth and Shattered Halls at their respective levels, they barely live up to the name.
Cataclysm
And so we look at the Catacylsm model - the intended drive back towards attuning yourself and being prepared to face heroics, that bear not only the title, but the mechanics, the expectation and the content of actual heroic instances. If the normals pose a challenge and require you to learn the encounters, asking you to utilise all of your skills (and skill), then how much more so will heroics be a real hearkening back to the challenge they were when first introduced.
Conclusion
How does this make you feel? Do you look forward to actually having to run the normal modes of dungeons a few times to get gear and experience in order to be able to tackle heroic modes? Do you think you will spend a lot of time running heroics in Cataclysm? Are you likely to stick more to guild runs than pugging or do you expect the skill level of players to increase on demand?
Sink or swim, there is definitely more of a challenge ahead. And it is good.