CUD

They add a saddle formation mountain range with multiple peaks complete with a couple caves to go in the place of what was an occlusion shortcut (A large more or less featureless mass designed to allow the cpu to occlude, or not have to draw the geometry behind it, saving resources like draw calls and polygons), requiring the engine to now take a double hit on resource draw, there is more geometry to draw than before, not just polygon crunching, but actual draw calls as well, AND a large 'cheating' landmass that was simply there for occluding geometry thus saving resources, has been redesigned, with traversable land leading to a cave, AND showing the geometry behind it, which makes the scene far more demanding than it was before. Not to mention increasing the lod in general throughout the entire scene, well, what you can see through the downsized res and lossy compression anyways. Its considerably easier to see those in the actual videos.

As for the first trailer, everything thats been shown since craps on it from space man. It DID look good back then. But it had a lot of shortcomings we thought was the price to pay for a game that size, that have been curb stomped by the latest builds,blowing expectations for ('good for wii u' away.

In the first trailer, the character is shown traversing the side of a lake, a lake made with three very distinct vertices, it was a noticably angular ake, not uncommon for games of  large scale last gen.

Here you can clearly see the individual vertices used to change the lakes angle. This right up next to the lake, so this was the highest lod you would see of the lake. It would have the most polygons used than you would see from any other distance.

Here you are hundreds or even a thousand feet above a lake, clearly a situation where you use a low lod, and it has smoother higher polygon edges than the high lod lake modeling of the first trailer. Its a pretty huge difference.