The way I see it, a hardcore (or core) game is one where the player makes a significant investment into the game whether that be in the time it takes to play through (e.g. sandbox like GTA, Skyrim, most strategy games like Civilization or Starcraft), an emotional investment with the story/characters (e.g. RPGs like Dragon Age or Mass Effect) or in attempting to master the mechanics (God of War, Mario). They're essentially games that require the player to immerse themselves into one or more of these aspects to get the most out of it.
That's not to say a game can't be both casual and hardcore as games like GTA, CoD and Mario can be played casually or a player can invest and immerse themselves into the game. Bridge titles that balance both core and casual elements are what developers and publishers really strive for but rarely succeed in.








