I don't remember either Quake or Worms being set in a WWII trench :P
Anyway, no you couldn't wander around the level - there weren't even proper *levels*, you were pretty much stuck inside the trench, being able to move either left or right to avoid enemy attacks. Perspective was neither isometric nor flat - I can provide an example from
this NES game which used a similar one: basically, you could see your character from behind.