Ok first off this post is going to have SPOILERS. So if you don't want to hear about them or see the ending cinematic for Cataclysm please stop reading. I don't want to hear about how I ruined everything for you. I said it, but will say it again. This post contains SPOILERS. That word again was SPOILERS.
Here is the cinematic
So the age of mortals is upon us? Well I completely understand that this was the perfect point in time have to the Aspects powers to diminish. Why you ask? For the simple fact that Deathwing is gone. The last tie in for the Aspects themselves. Now I think many people will misunderstand what them losing their power means. It doesn't mean that they are dead. They are still dragons and extremely powerful. They are like the other dragons that exist throughout the world. They now are not demi gods that can pretty much do anything. They have a lifespan, and will not live forever.
Also I very much enjoy that the mortal races will now just not run to the Dragon Aspects for help every time there is a problem. If you haven't realized the mortal races have done a lot to ensure Azeroth's survival. This now is the realization of everything, which has happened and everything the mortal races have done to make sure it has.
Thrall and Aggra having a baby fits nicely into the cinematic, but I am not sure it was needed. Not that I am against it at all. It basically comes full circle with everything that was done during the elemental bonds questline. I just hope Aggra isn't pregnant for years like Auduin seemed to be 8 for 5 years. As long as they don't mess this up it works.
And lastly, I think this really is a good way to be heading with Mist of Pandaria coming. Remember the entire expansion is going to be about the War between the Horde and the Alliance. With the Dragon Aspects not there to keep the mortal races in check both will be pushing back and forth to see who gains the power, and that leads us to the Pandarians who will teach us that balance is and always will be the most important thing.