These are a few Work in Progress shots of a Cry Engine 3 demo map I am working on right now. The engine is powerful and has a strong focus on environmental scenes with loads of flora and a mixture of buildings.
Although nature scenes are interesting, the more challenging part is the combination of powerful tools like the Foliage Tool, Terrain Tool and normal assets. Using a strong decal and spline system, only a few castle assets (four for those with a keen eye) can be used to make a lush complex environment without falling victim to repetition.
The editor is strong and I would definitely advise it if the project focus is on nature with some sporadic buildings thrown in.