We (2 50s parents and 2 18yo children) cruised on Oosterdam for two weeks, joining about a month after her return to service. Overall, this was an excellent cruise for us, and we actually think it was better than our 25-day 2019 Mediterranean cruise on the Koningsdam. We selected the cruise primarily for itinerary--lots of ports, and places we mostly had not visited previously. With one exception, we took independent excursions, and generally aimed to have at least one meal ashore wherever we went.
Capacity & COVID
The ship was about half full during our cruises, but it felt less crowded. We never waited more than a minute for an elevator (even when returning from shore), and rarely even had to share one with other guests. Lines for food were always reasonably short. In the MDR, only about 1/3 of Deck 3 and perhaps a bit more of Deck 2 were used; diners were not dispersed (but you could request to be located apart). On the downside, some of the entertainment sessions lacked energy because there wasn't enough of a crowd. We happened to be near one of the COVID isolation areas on the ship (blocked by a firedoor), and I would guess that perhaps 5-10 rooms were used the first week, and somewhat more the second. No official mention was made of COVID cases that I'm aware. Some (but few) passengers masked, but all crew except officers wore masks inside. We had no issues or complaints with COVID-related embarkation requirements (in our case, a recent 3rd-prty validated negative test, plus proof of vaccination).