Actually, my experience has been that the food and service in the main restaurants is just as good (or better) than it ever was, and of course, there is no cover charge. The only restaurants that carry cover charges are the specialty or alternative restaurants on most line's ships.
These would introduce fine dining with impecable service that is a notch or two higher than the main dining room. It is just another option that did not exist before alternative dining was introduced.
No one has lost anything, simply gained more options. I am sailing on the Norwegian Star in Alaska in a couple of weeks and can't wait to dine in Le Bistro, The Soho Restaurant, the Tepenyaki Room, the Ginza and so one. I could dine in the main restaurant every evening without paying extra, but to me the dining experience is worth it.
Just my opinion
Give it a try, I think you will like the experience.