My wife was on Oceania earlier this year and I was on the Regatta a couple of years ago.
will lead you to my wife's review and
will lead you to mine. I found Oceania to be a great value. The restaurants were excellent and the food and service typical of a luxury cruise.
We never had a problem gaining entrance to any restaurant. I am not sure of your itinerary, so I can't comment on the ports. Are you doing the Eastern or Western Med?