I love Fire Ready Aim! Billie's high pitched angry singing in the verses is awesome and super cute . There's something really enjoyable about the melody/tempo/singing combo. I love when it comes on when I'm running, it's nice and catchy and energetic. I'd like to see it live, I'd accept it as a Know Your Enemy replacement.
Honestly I just like the shark thing with Here Comes the Shark Shock, that's pretty much the extent of my enjoyment of it. I still think it's just standard b side/didn't quite make the album material though, not indicative of anything terrible.