I think if someone plays a specific game to the fullest and tries to do every little tiny thing in it (records, beat the game perfectly and other things) that means they are a hardcore player of that game. I'm sure there are people who are hardcore bejewled players on their cellphones, that doesn't make them hardcore gamers.
A hardcore gamer if I were trying to explain the term would be someone who plays a lot of games, usually has a decent variety of game types or genres, has a few game franchises that he or she is totally a fan of and doesn't purposely avoid a specific console if it can be helped.
Basically someone who loves games, not just specific games but games in general and so is interested in lots of games that he/she finds interesting and doesn't stick to just one game or genre.
Also I think a real gamer wants to support original games that they think are underapreciated or fail commercially while being great. I also think a hardcore gamer while of course experiencing the fun in playing a game, he/she also wants other qualities and depth usually. By default this person wants to play as many of the games worth experiencing as possible, regardless of console or machine.
Thanks to Blacksaber for the sig!
