In that case, ill give you a run down of the main things I see
First off, its mostly like normal terror, yes, but the 2 stage makes it very much 2 fold in potency : twice the number of civilians to die, twice the blow at failing. Usually I end up with something like 16 civilians dead, which is 300 or something, then the amount of kills make it SLIGHTLY better, but not much
The caves are the worst, as its VERY CQC oriented, giving the spiders an immense advantage. I think if you could generate it so you start at the "mouth" of a cave, it would be better, rather than surrounded on all sides by spiders. Both times I had 1 agent on each side, hoped for the best, and got wrecked because spiders on all sides, and with 4 people, this is too much.
In retrospect, maybe making the cave entrance a bit more like an entrance to a bunker would be better, but with a hill going down into the cave? Just something so the player isn't absolutely surrounded when already weakened, and with no visibility. Because this is the biggest thing, the caves are so narrow and winding, your fucked if you have people with reactions sub 60... maybe making the caves more open would be better, as on average they are 1 - 2 tiles wide, and very twisting which limits visibility to something like 15 tiles out of the gate