In order to introduce fresh air in missions that consist in run to a point killing every ennemis in da way, it could be cool to have some mission event (not condition) very different from each missions to make more gameplay variety…
Let me give you some exemple :
In a mission where we have to retake an outpost controlling by ennemis, it could be nice to have a segment of this mission on a bridge under the fire of ennemis artillery ! In term of gameplay, we would have to run in cover when earing artillery fire, otherwise we should be annihilate by massive explosions !
In another mission, heretics could have trap the area with explosives (love explosions) forcing us to run really fast in an epic obstacle course full of poxwalkers while heretics shooters try to kill us from distance ! It could be set on a bridge too, collapsing behind us running for our lives !
Something like dat could make mission really cool !
Those would need to be new mission outright (At least if they change the locations and stuff, none of the mutator change the map itself)