I've never been a big fan of HC previously, but I'm really loving HC TDM and KC in Black Ops 2. First thing, there appears to be next to no lag, even when I'm playing with a full party (my friends and I always find the connection in core terrible in a full party), Secondly, since everything pretty much insta-kills in HC, you don't really put yourself at any sort of disadvantage by using any weapon you feel like. This could also explain why lag is not so apparrent. Even if you do die a BS death, you'll never know because there's no killcams. My friends and I had all but given up on playing in a party and now everyone is logging on daily for a decent length session and having an absolute blast win or lose. This game is definitely better played with a team who care about trying to get the win and HC has made that possible. Consider me converted!
I've always liked HC to a degree, but I play almost all HC when I play BO2 now. Mostly because of the isses with the lag you mentioned. It's not so apparent.