"Great ideas are often inspired by other good ideas. When you take someone's design and change it to improve it, its called progress. When you take someone's idea and use it without changing it, its normally called plagiarism or common theft. There is a certain amount of flattery involved when you use another's ideas. Use plenty of ideas from others and mash it together and you might even be able to pass the similarities off as coincidence. In the case of Dark Void, the developers surely took a lot of great ideas and tried to pass it off as a wholly new idea. Problem is, when you mix peas and carrots you don't get parrots. You end up with simply peas and carrots."