This statement surprised me. Is it really true? It appears that there is conflicting precedent:

"The first approach is from the 2nd circuit "The Subtractive Approach" (Altai, Nichols) and the other approach is "The Concept and Feel Approach" (Ruth Greeting Cards, Krofft)"

http://www.newmediarights.org/guide/legal/Video_Games_law_Co...?

I am curious to know what would happen if someone decided to clone the exact level design of a game but changed all the audio/visual assets.