This doesn't really fit with what i've read in this thread so far.
So a few of them get together and make a copy of your game. It's got the same gameplay elements that they liked in your game, but uses different art and a new engine.
So then it's not "my" game then. If you've made a knockoff that's still a completely different game because you've put a lot of effort into making it. If you look at the efforts of something like OpenMW in which they're trying to make an open sourced version of Morrowind with the same art assets, it's taken them years to complete and they're no where near done yet. This is the exact opposite of copying a game and pirating it which takes minutes without DRM or a few days with it.