I took these screenshots for my recent presentation on the 8th March to show similar outcomes my environment could look like. Mine will of course have distinct features but it is nice and interesting to compare other successful games to each other. The first 2 screens are Skyrim and the other 2 are Black Ops 2 screens. They are 2 totally different games with 2 different paces.
Skyrim pictured above is open world so you have vast calm landscapes showing variations in changing land from barren land to more busy foliage. For them to blend well and look good is important as you will be going over these lands again and again, backtracking or looking for secrets.
Black ops above, on the other hand provides a very populated and closed in land with a linear path to follow meaning less exploration. You could take your time to look at effects but if you (like most normal people) will be focusing on the mission you may not spend any more than a minute in that certain area. In that case you can add more effects and assets to make the area look good but you can also skimp on the LOD of some objects in the distance and reduce texture sizes and extras if they will be easily ignored. It also depends on what the engine can handle too of course.
Since my level has a single path (section 1) leading to a slightly open path leading to section 2 and 3 i could block off the surrounding terrain around the path or open it up to make it slightly explorable. To begin with i will make the path linear but if i feel comfortable and i have time i will try to open it up a bit.