I personally love it, the harder the better. I love him pinching, sucking and even biting my nipples. I have even been know to cum by nipple play alone, takes time but really turns me on.
Nipple tweaking, twisting, licking, sucking, biting or slapping is a massive turn on for me. Love having my tits ripped from my bra and feeling the material scrape against my hard nipples.
So far as I am concerned, my nipples are a sensitive part of my body well connected to my genitles. When my nipples are pinched, sucked or bitten (even by my baby while breast feeding), I do get so aroused.
Never tried but I've even read that many women can even orgasm by playing with their nipples.