RAAM is easy, just torquebow/frag and headshots.
The wretchs i actually find funny cause you shoot one and roll away melee anothr then rol and chainsaw another, roll just after killing it to evade damage, the hard bit i think is where you ar outside Marcus' house,(act 4) and you have to go to he A.P.C and you have 30 seconds after you kill the first 2 Boomers, you either get shot or run out of time and the Brumak (wtf is tht?) destroys the A.P.C