I think on balance the majority of people feel quite positive about P&O: and it’s the same with all the other lines I follow on here. In fact it seems sometimes that complaints from some are met by cheerleading from others. there are the occasional whinge-fest, but predominantly it’s pretty balanced.
People talk about “the good old days” but for me personally we cruised with P&O for the first time over 10 years ago and thought it was dreadful and didn’t go with them again for many years. I now think they are great: they provide decent ships with a good options for evening entertainment, to good destinations at a very competitive price. My only slight criticism is that the itineraries are very static and a bit of variety would be nice.
P&O aren’t promising anyone a rose garden, it’s not a 6* line, and sometimes they don’t do things right, but overall they do a decent job - quite clearly so considering they manage to fill so many ships with so many people on a frequent basis!