We just got back from 7 days on the Sirena and had a great time. It was our first time cruising with Oceania so didn't know what to expect.
Pros: very nicely decorated ship and easy to find your way around. Very friendly staff and food was excellent. State room was very well organized with lots of storage. Very nice not having to pay extra for sodas, specialty coffees and specialty restaurants. There's a free laundry to wash clothes. There were no children running around and screaming. Efficient embarkation and debarkation.
Cons: the cruise was much more expensive than what we're used to and not sure it was that much better. Food is not always available as on other ships. I went looking for something to eat about 3:30 in the afternoon and could find nothing. Most ships have at least burgers, hot dogs or pizza available 24/7. The bathrooms in the state rooms are very small. They say they are eliminating plastic from the ships but still have the little plastic bottles of shampoos, etc in the showers. We encountered several very grouchy fellow cruisers and have not encountered that before. I'm guessing it is because of the higher socioeconomic status of most guests. They seemed very entitled. The entertainment was average. Nothing really great. There were also very few places outside on the decks to just sit and relax and it was always difficult to find a seat by the pool. They cater to a much older crowd. All in all we had a great time but again, it was quite a bit more expensive than any other cruise we've taken and not sure it was that much better.
Nicely decorated with lots of storage. Comfortable bed and nice balcony. Bathroom and shower are very small.