Stonefalls
Without a doubt one of, if not the best zone in the game. The trees come with naturally little foliage, and are often replaced by giant mushrooms. On all scales, the vegetation is varied and detailed. The rock formations remain a weak point, but are also very reminiscent of TES3.

But where Stonefalls really shines are the atmospheric weather effects. Ash storms between ragged mountains create a dynamic distant fog, ash and sparks from the volcanoes tumble through the air.

Just one more because it's so nice.
Deshaan
Deshaan keeps some level of dusty fog, which helps to hide its weak aspects of large, sparse trees and low-detail rocks.

However, the alien and varied vegetaion also contribute a lot to the zone's atmosphere, even when the polygon-count is low.
Shadowfen
In many areas, Shadowfen feels the most like a real forest. Here the vegetation is quite dense, trees of different height and shape cast shadows on the swampy ground. The density is enhanced by the low view distance due to atmospheric fog.

This creates the illusion of actually being lost in a dangerous swamp; additionally, the low quality foliage is hidden behind fog or hard contrasts.

The already great level of detail on the ground is enhanced even more by water reflections, which almost gives Shadowfen and unfair advantage compared to other zones. Overall it's just really well done.
Eastmarch
Eastmarch is a mixed bag. The volcanic tundra has the strong points of Stonefalls and Shadowfen, due to its atmospheric fog and water. The trees are varied, foliage is either absent or hidden in the fog; against the sun, they stand in sharp contrast as silhouettes, enhancing the mood greatly.

Problems show in the "green" areas, where sparse large pine trees stand between low-quality rock formations. ESO's weakest points are combined here with little to make up for it.

This is one of the better green areas, showing more varied lower vegetation and denser trees - although they could still be reduced in height and increased in density.

While snowy areas don't have better trees, the snow adds a better level of detail to textures, and some blown-up gusts of snow add to atmospheric effects.
The Rift
The Rift looks great in areas with dense, low-height vegetation, especially birch trees. In these parts, the atmosphere is very reminiscent of TES5, not in small part due to distant fog of a certain hue.

Where the Rift struggles is in areas with larger, more sparse trees and open spaces without a lot of detail on the ground.

And this not only concludes the Rift, but our little tour through Tamriel!