Two main problems with the HMMWV M2 gunner position.

1. While you can change seat from driver or passenger seat to gunner seat by looking at the gunner station and holding the appropriate action, there is only one way out of the gunner's seat, and that is to exit the vehicle to the roof. There should be a way to move from gunners seat to the other seats, if empty, without leaving the vehicle.
2. This is more of a missing feature, which is to duck most of your body inside the vehicle without leaving the gunner seat.