All of my cruising so far has been done on Princess, so I'd have to say that I do tend to like them
. I have to admit, I'm a little surprised at the "Ive not heard anything good about Princess", because I definitely wouldn't consider them to have a bad reputation.
From what I've heard, I'd say it compares reasonably with Celebrity, some will pick one, some will pick the other, and it depends on what people are looking for in a cruise too. Holland America is also pretty similar. They're all mass-market cruise lines, and these days, you're definitely starting to see the places where the lines are starting to cut corners to keep the fares down, and as a result, you're seeing more nickel and diming on all these lines. Princess is definitely more low key when it comes to onboard activities compared to something like Royal Caribbean.
Princess has been fragmenting somewhat when it comes to regionalization. I know there's a number of ships that operate the Australia market, and the onboard experience is different for those. I think this has been happening with the Asian market for them too. I'm pretty sure the Diamond has undergone a number of changes specifically for the Japanese market. I can't really remember exactly what they were, since I didn't pay a lot of attention to it, but one thing I vaguely recall is the installation of bidets on the toilets. I think they also added a sushi restaurant.
I think if you were happy with the experiences you had on Costa, Holland America and Celebrity, you'll do fine on Princess. One thing with that ship - almost all of the mini suites are on the the Dolphin deck. As a result, the balconies are all completely exposed from above - if you look at how the cabins step down the side you'll be able to see this. There's a handful of mini's that have completely covered balconies on the emerald deck, but they're also right over one of the entertainment venues. Suites I think are mostly on the front or back, and the back ones at least would be completely covered balconies. Caribe deck balcony cabins tend to be fairly popular, they have larger balconies, and they're about 50% covered.
I think I'm around 192 days on Princess, so at least from my perspective they must be doing something right.