We've cruised about 20 times and had sailed with Oceania twice in the past, including another cruise on Riviera. We absolutely loved it. Oceania had become our favorite cruise line. Not any more. We were among many passengers we spoke with who felt the same way.
Always known for outstanding food, that's no longer the case. Perhaps half of the time the food was very good, The rest of the time it was very average, far too frequently bland or over-cooked. The buffet was especially boring but even the speciality restaurants were disappointing.
The ship itself was often unpleasant. It was so cold in many of the public areas that we simply couldn't stay in that venue even though we were dressed in warmer clothing. They actually were offering blankets to guests in Red Ginger restaurant.