I have to qualify this response by saying that I have not sailed on Oceania but I did sail on Renaissance which was headed by Frank Del Rio and used the same ships.
One thing to look for in any message board threads or cruise reviews are recurring themes. You will always find reports of stolen property, lost baggage and other negative issues no matter what cruise line it is. This is true from the most luxurious to the most mainstream.
Take in all information before making a final decision.
I personally cannot wait to try an Oceania voyage. The size of the ships, open seating and port intensive itineraries are what appeal to me. From what I have read, and I have read a lot about them, they seem to have a good customer service reputation but very overpriced shore excursions. Those two themes seem to come through from my perspective. First hand cruisers will probably have a much better perspective.