This was our 21st cruise. We have sailed on Costa before as well as the other "main-stream" lines, e.g. RCCL, Celebrity, Norwegian, HA, MSC etc. This cruise was a last-minute replacement for a cancelled MSC cruise. Essentially, we paid less than 50% for the "same" cruise on Smeralda.
We had read the numerous reviews on here and we were not unduly concerned since our own experiences have never been at either end of the extremes when we have sailed on "terrible or excellent" ships.
The first thing to mention is the efforts that Costa have gone to to cope with the pandemic. You are tested before getting onboard and at least twice again during the cruise. This takes no time at all and has effectively no impact on your cruise. They have installed hand-washing facilities in all the restaurants, sanitising stations everywhere [always full] and temperature stations everywhere and you were obliged to take your temperature every day. Mask wearing onboard in public areas or when moving around was 99.99% compliant and was enforced. Everywhere, staff were cleaning constantly. The buffet was served to you and again, great expense in putting glass screens all around the food [indicating it's here to stay].