Out of the many inventive mechanics we've seen over the years, some have been woefully underused or under appreciated by other developers that could have added it to their games. Of those these rank at the top of our list as five innovative gameplay features painfully ignored by other developers.
Those were all good features but you can't say companies are ignoring implementing these as all of these were unique to those games.
Discovery mode in Assassin's Creed would only work in historical accurate games.