We have been on the Caribbean Princess several times, the latest 18 months ago. Was it brand shiny new? No, but it was in great shape, no smells, everything worked fine and it was by no stretch of the imagination Dirty! The staff and crew were great! There was always crew, cleaning, painting, etc.
We have sailed on Carnival, Royal Caribbean, Cunard, Celebrity, MSC and Princess. They all have their good points and not so good. Newer ships tend to be nicer unless they are brand new like the MSC Seaside when we sailed on her....lots of issues. So it can happen on any ship just like any hotel or resort or airBnB.
For families, Royal is probably a good choice with their waterslides, rock climbing walls, surfing, etc. But when my DH and I sail, we want fewer kids, less playground atmosphere and a bit more refinement than Royal (we're Diamond on Royal so we have sailed them plenty of times)
With Princess, sure the newer ships are nicer and in perfect shape, but all the other ships are well maintained (with one exception...the Crown, but only on our sixth time on her).
So everyone is looking for different experiences but for us at this point in time, we prefer Princess. We love the ships, the itineraries are great and varied, the crew is wonderful and it feels like home to us!