I thought I'd add our QA dining experience to the thread.
We're on board currently ( Norwegian fjords).
The first 2 nights we did open seating upstairs, and were really disappointed. It was super busy, with a queue to enter at 745. The waiter was so busy he didn't introduce himself or chat, and the wine steward was rarely sighted. I managed to get only one glass out of my white wine bottle each night. My wife ordered a cocktail and it never turned up.
We shifted to the 815 downstairs sitting last night and it was chalk and cheese. The waiter was joking with us ( we had him serve one of our friends double portions of everything). The wine waiter was there from the start and found our bottles from upstairs, also arranged the cocktail promptly.
I was amazed at the different pace and atmosphere downstairs. That had been my only real complaint about the cruise so far - so very happy now.