Went on one with Royal Caribbean over Xmas with the gf.
From Sydney up to New Caledonia and around two other islands. 9 nights with three days on shore.
We liked the three day stop offs, but unless you booked a trip there wasn't a lot to do on two of them, but the trips we did were excellent.
All the staff were excellent, majority from India or Malaysia, overall very good standard of English spoken and very helpful. Ship was cleaned immaculately 24hrs.
Didn't like the two day travel between Sydney and NC. Too long for the limited entertainment on board for people our age (late 20 early 30). Once you have done most things once you wouldn't do them again so towards the end of the holiday you were a little lost, mini golf, cinema, climbing wall, etc etc. Good gym on board, with classes available at extra cost... Spin bikes only to be used in classes so I had to make do with the standard crappy exercise bike, I wasn't paying $15 for a group spin class.
Activities were aimed at either kids, or retired people IMO. Card games, bingo, dancing etc
Lots of pool activities for the kids and the crapper games, best bellyflops competition etc.
There was a show every night, but these didn't appeal for us. Excellent range of dining with 6 or 7 different restaurants, most come at extra cost, but the inclusive dining was very good, and the extra cost was only $75 as a package for 4 of the restaurants.
When you get on board they try to fleece you to buy a drinks package which are a daily rate of something insane. Buying drinks on their own was very reasonable, water, orange juice, cordials were all included, coke and alcohol wasn't, $6.50 approx for a beer which is comparable to Australian pubs.
You could tell it was very americanised, quite a lot of pay to play things, casino, video arcade, lots of activities you had to pay for too. Also all the pricing on the ship was done in USD, so you had to multiply by 1.15 and then add 18% service charge which pissed me off! just show me a price.
They also took your card at the start and said they would charge your account at the end of the cruise which was fair enough, I knew what we had budgeted and could move money about if required on the day as I would have mobile coverage near to land. What they didn't tell you was they keep preauthorising your card daily wiping your account out. Getting a letter on Xmas day to say my card had declined and could I come see them riled me up, no way of checking my balance unless I wanted to pay to use their internet at almost $2 a minute... they ended up over charging me in the end, and over 8 days later I'm still waiting for some of my preauthorised money back!
Overall I would possibly do one again, if it was around the Med or somewhere which stopped off at a different location every day so you used it more like a moving hotel then it would be better, depends on the clientele.