Yeah, if I made Tetris and decided not to sell it, then saw all the clones, it would make my idea worthless.
Minecraft is another that could have probably been patented, if Notch didn't become a billionaire and someone just cloned his idea and became more popular than the original work, it would definitely be another point where patents could have protected his idea.
both cases worked out, the biggest problem with the first one was Russia thought they owned Tetris, so it wasn't quite as great there.
The one good thing about this particular case, is that I don't think anyone has used the system, and the game's idea has been out for 8+ years now, they can form an identity out of the idea, but I do think limiting it to 10 years would be better, however we are never going to have patent laws that make sense, so I guess we just sit back and enjoy the ride here.
My last feeling that I've had on this is that I don't really want the industry copying everything, I want there to be unique stuff from unique studios, and something like a 10 year grace period would benefit that, but it can't be vague stuff like NPCs remembering you, so I hope that this patent is very hard to generalize, and you really have to be making shadow of mordor with a different skin/setting/theme, for the patent to really come into effect.