Fist my definition:
Hardcore = You have to play it for DAYS to be good enough to pass the stages
Casual = You can play it a little and enjoy the game without have to master all your padawan skills first.
So, for me, the NES Marios was hardcores, than it become a bit more easy and better. So Mario Galaxy isn't hardcore, and I prefer it that way. Hardcore games like Tetris, Zack and Wiki, MMOs or No More Heroes are a pain in the ass when you can't figure out how to do some think difficult or how to kill a vicious boss or make 5000 lines and break you brothers record...
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