The SMAW on Serenity is definitely one of the worst. Its such a large map, so you have to traverse a large distance all the time, and you can't always check every corner, its more important to get to the front line. But at the same time, its easy to get to the opposite side of the map. That coupled with all the hidey holes, and you get smaw users who just wait for you to run by.
Also, frag grenades. They suck w/o any perks. You have to be kissing them for them to kill you. But with both ballistic perks, the kill radius is silly.
Not exactly OP, but the difference is like night/day.