The first part of the level is a mission to blow up the dam. The second part is the player escaping the dam. The underwater part is completely dark, there are no guiding lights and the player has to seek out air bubbles to breath. Why didn't they give the player a scuba gear? Or even personal submarine? The swimming speed is also low, which further adds to make this level unfun, maybe even unbearable.

The issue here is not that the level is underwater. It's about how are you expecting the player to have fun here? They just threw in darkness, oxygen, exploration, enemies, a boss battle and placing underwater bombs all in one level without caring about the player's experience at all.

This whole underwater part is a challenge. The player is supposed to follow the yellow pipes because that's where the air bubbles come out from. However, there are some valves that the player has to operate to redirect the air flow. Upon operating one the air is redirected and new spots of air bubbles show up, indicating the player's path. The problem is that the speed at which Duke turns the valve and the speed at which the oxygen meter drains wasn't carefully thought of to make the player's life easier or more comfortable. The player does have night vision with unlimited batteries, but the night vision is not anywhere as good as daylight and the air bubbles are much harder to see underwater than lights. The challenge itself has a feasible concept, the problem is that it isn't fun.