Long before Descent was released, i use to play advanced heroquest.
Descent is of course way better than the other one but there was this tiny rule that i liked.
Namely when heroes opened a door, they had to roll a die to determine if the heroes are surprised or not.
This created occasionally amusing situations and was for the overlord an advantage (at times) to have an edge over the heroes.
Where in Descent, the overlord allways has the last turn, and in most cases this means that the current room is cleansed by then.