AS far as food and service I think Celebrity, Princess and Holland America are just a little bit better but not by that much. Celebrity and Princess ships are more reserved and nicely decorated. Royal Caribbean ships are more glitzy, with lots of glass and brass.

I don’t know that I can give you a listing of good vs bad but I do enjoy Royal Caribbean cruises and I think they are worth the money. Their prices are comparable with the other "mass market’ cruise lines that I mentioned above.
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experience of many cruises

I’ve also been on the Caribbean Princess to the Eastern Caribbean and the Carnival Ecstasy to Cozumel & Progreso.

Of the three lines, I definitely prefer RC. The ship layout on Caribbean Princess made it seem really crowded, and the decor on the Ecstasy was too crass and gaudy.
But I’ve enjoyed every single one of my cruises! and definitely thought they were worth the money. If you’d like to see some pictures (including onboard), go to roofingprincessmos.shutterfly.com
Bargains can be found on many cruiselines if you can be flexible with your vacation plans. If you don’t know much about cruising, it can be helpful to find a good travel agent who does (not an online agency).
One of the good and bad points about cruising is that you wake up in a new port almost every morning; it’s good because it gives you a taste of a lot of places, and it’s bad because you don’t get to spend enough time to really get to know any of the places.
I like the fact that I unpack once and get to see many places, and that my meals are all taken care of.
As for shore excursions, if you can do enough homework, it’s possible to arrange them through private vendors instead of those on the ship; the number of people on them is generalllyl smaller and yet the price is also less.
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