I created this scene in Unreal 4 and I was keen to experiment with the new volumetric clouds and also further utilise the procedural tree and foliage placement tools. I used nature and castle ruin assets from the Unreal marketplace.
Volumetric Clouds: The clouds were created using the new volumetric cloud plugin and I have to say it is awesome. You can create any type of cloud formation and also layered clouds on top of each other if need be. There are some drawbacks though and it's an expensive resource for a game to run and at the moment it's unlikely any game will use them running at the highest settings, but for cinematics and cut scenes, they work really well.
Trees and Foliage: The trees and shrubs were all placed procedurally - and is a straight forward process in Unreal. For a large landscape, I would definitely always do this procedurally. It's super quick to set up, and only covered the area of the landscape I specified. It also gives more control in post-placement of the foliage, so for example, after generating the foliage you can still amend clumping, density and other settings and then regenerate (until you get a look you like). As opposed to painting on trees with the foliage brush, and once painted you can't update the layout, unless you remove and re-paint. Of course, both processes are useful in setting ways and if I wanted to create a very specific layout of trees I would use the foliage brush.
Landscape Grass and Foliage: The grass/flowers on the landscape were part of the landscape material and again were easy to update with different meshes. I tried about 5 different grass types and ended up with 3 combined types, including some poppy and white flowers.
Castle Ruins: I placed the ruins in a fairly sparse manner and also amended the world settings to maximise the graphics quality. Whilst amending the lighting I by chance found I great night scene. So I added in some lighting and the model of a Knight holding a lantern. The castle ruins were built by Denys Rutkovskyi, and he did a fantastic job.