Everyone will have their own opinions on what constitute a hardcore gamer. For me, the hardcore gamer:
1. Plays a game not just for fun, but for a sense of accomplishment. Hence, a game has to have a degree of difficulty that will challenge the game at every step. (Eg. Monster Hunter)
2. Plays a game for extended period of time, and doesn't care whether this action will be seen by others as unproductive or considered an individual without a "life".
3. Plays a game to experience its entirety, that is, aim for the 100% completion. Explore every corner of the map, open every chest, defeat every enemy, and take some screenshots to keep as trophies.
4. Probably hates the OP for considering his/her desire to be who he/she wants to be a form of 'elitism', the hardcore gamer, the consumer who wants to get every penny worth out of the game he/she purchased.
5. Hangs out on gaming forum with like minded gamers, and talk about ponies.
6. Hates casual gamers, and maintain a checklist of all casual game developers that should be eliminated from our lovely planet. > . >