Adding meshes and creating atmosphere is what he prefer. Creating a world, starting with nothing to end with a lovely universe and nice points of view. Giving a level the best interaction you can considering your mechanics, that is the most important point for William in level design.
By giving a great importance to Level design, William search the best ideas in game design to get levels as awesome as it can be and funny to play.
Seeing web development like level design, he likes to give life to websites, creating the structure and adding assets from the designer.