Well, IMAO (In My Arrogant Opinion ... I don't have Humble opinions) the food in the Main Dining Rooms has remained consistently high in quality. We have really seen very little slippage. There are two big exceptions, lobster and caviar. Aside from that we are very happy still with MDR food and would rarely visit an alternative restaurant.
The biggest exception is Sabatini's on Princess! This not just dining, it is an experience! So we do make a reservation there every trip.
My wife is also a fan of the Pinnacle Grill on HAL , me not so much.