A hardcore gamer is a gamer who is not blinded by nostalgia. A gamer whose abilities to discern childish, mindless fun from deep and intriguing entertainment far surpasses that of a casual gamer. A gamer who recognizes that sheer content and gameplay falls flat if a video game's visuals are not up to par with today's standards and expectations.

Truly, a hardcore gamer is a respectable gamer. A gamer who does not let immature temptations sink their reputation for good, and who acts their age.

For me, mature gamers = open minded peeps, hardcore gamers = addicts.

Edit: did not read clearly dangit, mature games = have sexual and gore content 

I don't really get how pikmin has a mature plot.  Pikmin definitely didn't have much of a plot, seemed pretty bare bones.  To me (and I assume most people) mature can mean two things.  1, that it is fully developed, and 2, meant for older audiences/ not suitable for children.  I don't think you could apply either of those to pikmin plot...  I can definitely see the hardcore gameplay argument though...

Hardcore Gamer = A person who plays games for the challenge. They play games as a serious hobby, not just for pick up & play fun.

Casual gamer = A person who plays games just for fun. They don't take it too seriously & uses it just like they would a movie. It's just entertainment

Mature Game = A game that's not family friendly. Can a little girl watch you play it? Would you feel comfortable playing the game in front of that little girl? No? It's a mature game

Non-mature game = A game that anyone can watch / play without feeling uncomfortable in any way

My view

Hardcore gamer = you and only you and everybody else is a poser.

At least the word is largely used this way.

A "mature" game is the opposite of an f2p game with flash(like) graphics, little substance and no definitive body.

A hardcore gamer is someone who enjoys his "mature" games of his favorite genre(s) to full extent.

well, it is a bad comparison to begin with if he is trying to remove the ESRB mature label as that is what most people are probably saying when calling Dead Rising 3 mature.  It is mature because of the insane amount of violence and vulgarity, not suitable for children.  I haven't actually played dead rising 3 so I can't really comment on that plot...

Hardcore isn't a genre or type of game, it's the investment you put into it that makes you "hardcore"

If you spend 18 hours a day on Candy Crush, I consider you more hardcore than the guy that plays 2-3 hours of Halo a week

It all depends on how someone views it since everyone's definition will vary. There is no certain right answer.

There's no true definition. A game is only as hardcore as the gamer perceives it. Someone might find Destiny to be hardcore while I think Fire Emblem: Awakening is. In the end, it doesn't matter.