The hearts for necro sound more fun than the ones for the rogue, which almost all of them seem kind of useless. At least that's my impression at level 35.
That Necro heart that he was show casing is freaking amazing. This is my first time playing a Necro and I don't think I can play the class without it. It saves about a hundred clicks per minute.
Playing hardcore you need to set other goals than get this first character to 100. For me, more than anything, its about learning your limits at every stage of the game. Actually learning, getting better. Losing one character doesn't end that. And. Nothing beats the blood pumping because you are in a sticky situation knowing there are consequences. It's a thrill.
That said, I play both SC and HC. Mostly SC because I play late when I'm tired. So my HC progression is slow. Very slow. But I enjoy it a lot next to my SC main. No need to go all in. Think Ive died four times in hc before season 1. My biggest achievement so far is lvl 30 which is only a few hours of progression without death :)