So, my thoughts on Cataclysm:
1. It's Very Linear
It really is.
2. It uses lots of phasing
Finally, the actions you take actually have an effect on the world, despite the fact that there are 13 million other people running around. No more finding Manrik's wife, then watching him send other people off. Kill those nagas, and as long as part of a scripted bit, they stay dead. This is, of course dependent on the Linearity. It would be a nightmare to test all the possible paths through various levels of phasing if people could just do what they wanted.
3. It's very pretty.
Despite being remarkably old, I was sorely tempted to take some serious psychedelic pharmaceuticals when I first hit Vasj'ir. Look at the colours! whee! That's deep man.
However, that's not necessarily a problem, since the linearity allows for Story. Finally, your level 80 hero can do heroic level 80 things. You just can't decide what heroic things you want to do.