I prefer the term aficionado. 

The thing that is bad about some hardcore gamers is that they take the games too seriously. OK there are some things that annoy you in some games that other players do, calling them noobs etc that i agree. But I play games just because i have fun and i love playing them.
I don't get into lobbies and start swearing because someone doesn't know how to play a specific game well or because I think that because i am good in one game then i am superior or something!

Hardcore gamers should be hardcore in a good way and not ruin the fun of others

I have a Virtual Boy that I still play. I win.

I have a friend in my PSN friendlist who has over 50 Platinum trophies. :D

I beat all FPS's on the hardest difficulty without firing a bullet.  I play all JRPG's without any kind of magic.  I beat all Hack n' Slash games by only jumping.  I even got the highest scores on all Wii Sports and Sports Resort games, after I cut off my arms and legs. 

Also, like to point out that Lestatdark and nen-suer are pretty hardcore gamers (they always talk about very niche games)

I don't have a Wii anymore, therefore I'm a hardcore gamer now.

I really can't agree withe OP definition of Hard Core. That sounds very Casual. They are Casual about how much they play as single game. HardCore is those players that get insane scores that just boggle the mind. Hardcore is a <10m Super Mario Run. Hardcore is Billion Score in Bejeweled, Hardcore is the highest Score in DonkyKong. Hardcore is unlocking everything single achievement in any single 360 game, Hardcore is having a massive collection of games. Hardcore is NOT willing nilly changing game to game based on corporate media and sales pitches. That sounds more like Sheepcore.

If Hardcore was the definition of the OP. Then holy jeez I must be a god. I will borrow, play, buy almost anything game you can imagine. I got CCG, Board, RPG, Table top, miniature war, Computer, Portable, Console, watch so on and and so forth. I certainly don't limit my games to a small category. Anyways I will play anything, but budget is a constraint.

wait..... are we saying that the person BEATS these games or just plays them. If he finishes these games. Then yeah. He's HARDCORE game completionist.

hardcore gamers can be defined in a variety of ways.

I would consider your example as a hardcore gamer if gamerscore was indeed the most important thing to him.

I have a gamerscore over 45,000

pretty hardcore.