This was perhaps the most surprising thing for me too - just how little progress players make in each session compared to what I expected.
Also I was surprised by their interactions with NPCs. The first goblin they captured was made to lead them to his lair, whereupon his throat was slit. The second goblin they captured was made to march about in front of them as a trap detector before they eventually adopted him as their pet.
Huge importance would be read into random bits of dialogue, and I'd have to rework things to make that pay off for them instead of the thing they were supposed to notice.