Hardcore games

[Chrizum]

I still don't know exactly what hardcore games are... please help me.

Which of the following are hardcore games?

1. Tetris
2. Super Mario Bros.
3. Super Mario Galaxy
4. Commander Keen
5. Madden
6. Need for Speed
7. Halo 3
8. Doom
9. GTA IV
10. Rayman Raving Rabbids

Thanks.