Our first cruise with Oceania and we were really impressed with efficiency, productivity, service, "classiness", the sophistication of our fellow passengers, really everything was a notch above other cruise lines.
Riviera, as new ship, was fantastic. Cruise personnel were fantastic (everyone - from embarkation to room attendant to the lady cleaning the handrails). It was obvious that they've been properly trained to be up-beat, outgoing, friendly, helpful, nice to all passengers, all the time. So refreshing and pleasing to have happy helpful people on the ship no matter the situation or time of day.
In ports where we used tours from Oceania, the tour was great, allowed us to see the most stuff in the time allotted as well as get lots of background and information that would have been hard to get without lots of up front studying.
We downloaded Ricks Steves audio tours for several ports (Venice, Dubrovnik, Mykonos) and thought they were great.
Yes, we'd have liked more time in some of the ports, but that's the thing about cruising - you don't get to do 100% of everything, but if done well, you get a sense of what is there and whether you'd like to go back.