Any game can be "hardcore".
Many first person games (like Halo 3) can be played, and enjoyed by the general populace. When I took Halo 3 to a 5th quarter, post-football party, we had about 50 kids lined up to play it. Most of these people never played H3, owned a X360, or anything. Maybe 3-4 kids had played it before. Many just "knew" the game was alot of fun, heard about it, and wanted to try.
However, on the opposite end, some Halo-nuts spend hours a day on LAN parties and online multiplayer. They are hardcore.
The most important elements to a game being "hardcore" or not involve the fact if the game..........Has alot of replay value. You can play FPS, RTS, RPG, Sports, or any other game casually (once in a great while), or hours a day. World of Warcraft has 8m+ people. Some play for 5+hrs a day, some play an hour a week, and mainly play to socialize with friends and distant family (I have a 40 year old female co-worker that plays Everquest with multiple family members as a way to stay in touch with them).
IMO, there were alot of N64 games that were great games for both hardcore and casual audiences - like goldeneye, Super Smash Brothers and Star Fox 64, playing hours on end with a few specific people, and once in awhile with casual gamer friends.
Back from the dead, I'm afraid.
