Never stayed in these cabins as we prefer something mid-ship or if we were booking a C cat. cabin, we'd book one on the Lower Prom Deck.
If you are in rough seas, you will feel the motion far more being so far forward & high up. It might possibly be noisy being above the show lounge, especially during the shows or when the cast is practicing late at night.
Personally I'd choose another cabin, either on Lower Prom or Main deck. Actually the D cabins on Main deck are larger than the C's on LP.
To see what the cabin looks like check out HAL's website.
Click "On Board Ships", scroll down to Veendam, then click on Staterooms and choose Large Outside stateroom. there you will have a picture of the room.