I believe hardcore games are the guys who take serious, as in, the fun is welcome, but it's not the focus, the focus is the challenge. Sometimes taking the challenge is fun, sometimes it isn't, but they'll face it anyway. Which makes me wonder: what are you trying to prove? I mean, challenges in real life usually benefit you one way or the other, in professional life it makes you more experienced and gets you more money, a better position etc. In sports you get to become more healthy (unless you take it too far). In games... You get to display a virtual score? I don't get it.
The casual gamer will focus on the fun. I myself am playing Dark Souls, famously known as extremely hard (I insist though, Candy Crush is way harder), a "hardcore" game. I call bullshit, it's not a hardcore game for me, I just enjoy the game, and when it pisses me of I don't keep on stressing and jumping for success, I just switch games for something else, I play because the setting is awesome, the story is told in a mysterious and intriguing fashion, and the design of the characters, especially the enemies, is so damn cool! It also has one of the few "multiplayer" interactions that I find interesting.
