I find that actually pretty good. I even prefer it to the original which to me is total garbage and the song that ended Metallica's thrash metal career.
I'd actually say that these girls do, indeed, rock. Technically they are rocking. One need not always sound good to still rock. The vocals kinda killed it for me.
Not to be totally judgmental, but I didn't like it. Being a female, I should be supporting them, but the vocals are awful. Apparently I'm not the only one who thinks that.