I think there are two separate things that are sources of complaints with the terrain, which are independent things.
First, there is featurelessness of the terrain. This is an aspect of individual terrains and not any failure of the new terrain system. I looked at some of the island terrains offline when the patch first came out, and they were very sparse and of a uniform green -- not very interesting. But then I played on a terrain that was more filled out with different terrain features. It was gorgeous, such as the following pic. So, I'm not worried about this aspect.
Second, there are aspects of the brightness or contrast of the terrain. I think the terrain is simply not illuminated nearly enough. The sky is bright enough, but the terrain is too dark. This, I think, could cause some people to get headaches trying to pick out details among that dim background. Others can overcome it by turing up their gamma adjustments -- but that's not the best solution as things should be built to work with gamma adjustment of 1.0. If you then turn up gamma, some aspects can look washed out, and that also can cause some discomfort. Here is a screen shot from an earlier version of AH to compare brightness with the pic above:
