I am seriously disappointed with the way Blizzard handled the hard mode options for Uld, ToC, and, so far, ICC. When I think of the word hard, I think of something that creates a complex problem that is different from the normal way of doing something. I consider, for example, multi-dimensional calculus is harder than geometry. The only hard mode that I see fit into what a hard mode should be is Sartharion 3-drake and Flame Leviathan. In that fight, if done the correct way and not zerg'd, changes the simple tank and spank fight into a precision, add managing, endurance, and dps race. Flame Leviathan also falls into the same category. Four tower FL is complex because it took the tank and spank (which can be 2 manned on 10 player, and 5 manned on 25 player) and added special abilities, adds, and AoEs.
The problem is that everything after that point just doesn't seem to qualify as hard mode. In all fairness, a hard mode shouldn't be as simple as "oh you triggered me, I'm suddenly 30% more health and damage." Most notably Hodir's hard mode. It isn't a hard mode at all, more a faster dps race. Freya is just a damage and health bonus with a small slew of extra spells. Mimiron is creative, but his fight remains exactly the same save for the fires. Vezax is just an endurance test, Yogg is basically the same as the rest together, and Algalon, the hard mode only, which was just a fight of high raid damage with a limited number of tries. The hard modes in TotGC are much the same, just increasing the damage inflicted and the health of the bosses. There are few changes to the fight mechanics which basically make it simple.
Real hard modes should be something completely different from the original fight. If we can look at Mimiron for a second I can describe what would be a fitting hard mode encounter. Push the button and the fires spawn. In his desperation he brings out a machine not part of his original encounter, and maybe you would have to fight Mimiron himself, instead of just his inventions. He could fly around on a jetpack while the raid deals with the fires and the other robots. As a result, the fight mechanics completely change, thus rendering the fight in a much more difficult way.
Basically, to sum up my argument here, Blizzard has to design hard modes as more than an alternate fight rather than an augmentation of the health and damage output of the bosses. In a way to keep people on their toes and learning the fights, it should be something more than just "you'll have to heal your tank a little more, maybe even bring a third healer." They need to remember that the normal modes are geared towards casual players, and the hard modes are designed for the dedicated, highly skilled and committed players in this MMO.