I started out playing core back when I first got into COD when Modern Warfare dropped. I liked it. I saw it as the 'default kill & receive points' game type & played it through all of the CODs up until Black Ops 2. I started out playing core for about 200 games or so and decided 'Hey what the hell, might as well see what all the fuss is about with hardcore.'
My friends would always play hardcore & my little brother was always playing it too. I was, at first, not attracted to it because of the amount of 'camping' my brother & friends would complain about, even though I hadn't played the game type myself.
I gave it a try & I surprised myself at how good I was. I really adapted to it & my playing style from core transitioned to hardcore flawlessly, actually, it worked BETTER. The 'camping' my brother & friends would complain about isn't really an issue in my opinion. I just understand it's part of the game type & it's completely 'fair game' in my opinion. Needless to say campers don't really cause me too much trouble.
I feel like the gameplay hardcore is MUCH more fast paced than core. I would assume most people can agree on that point as well.
But uhhh, I really like hardcore since I made the transition. But I still do occasionally pop in core & wreck havoc.