They told me on my Level III course that Boeing first planned to leave the overwing exits on the 737NG as they are on
the 737CL. But FAA wanted that the door can be opened more quickly. Also it has to stay out of the evacuation way.
Now the overwing exit is hinged at the upper side and after unlocking of the door swings outside forced by an
counterbalance assembly.
But I think that Pictures are better than words:
Detailed view
Operation
View in open position
HIH
Ingo