We were also on this maiden cruise. We are not usually P&O cruisers (last one was on Canberra!! ) but are frequent Holland America and Celebrity cruisers. We were on this cruise to spend Christmas with my wife's parents who are dedicated P&O.
First, Christmas Day was a disaster - we were luckily on the first sitting but it still took over 75 minutes from starting to queue to ordering our dinner and then getting cold and tasteless food eventually finishing 3 hours after our allocated time. This they did improve fantastically for NYE where we did not see a single queue and we were served with good food on time.
A bit about ourselves to give context for my next comment - we left the UK 21 years ago to live in NL so maybe are no longer as British as we used to be. I wonder if having a cruise line that is only a single nationality is a good thing as all we saw were people looking for things to complain about (to be fair there were things to complain about) and seem to create a downward spiral. Also I have never met so many rude people on any other cruise as this one. I think if P&O opened up to more nationalities then perhaps the atmosphere on board may be much better.
Food generally on board in 2 parts - paid extra for was very good - Green & CO and Keel and Cow exceptional. MDRs were OK but well below standard of other cruise lines. Buffet was by far the worst I have ever seen on a cruise ship in both choice and quality.
We had a standard balcony for 3 of us and storage was a joke - not enough room, no drawers and very difficult to access when the sofa was made up as a bed due to the cushions from the sofa having to be stored in front of the wardrobe.
Musical entertainment was great but where were the art classes or the cooking demos etc?
Disembarkation at Southampton was a joke - 45 minutes delayed then long queues to get to the baggage and then a scrum to try and find your luggage and then another long queue to get through an unmanned customs area to join another long queue for a taxi. Celebrity Apex in July in Amsterdam this took 20 minutes in comfort - lots to learn for the Port!
Will we cruise again with P&O - no - there are so many better cruise lines with better offerings (Celebrity included wifi, tips and standard drinks package as standard at better price) and I would not go again on a single nationality cruise.