I agree with clairbearinaus. We've been to each a number of times. Mystery Island is a beach day. The other side of the island has great snorkeling. Port Vila has lots of options when you get there. We don't let the cruise-lines scalp us anymore. We've done Hideaway Island, that was nice. Last couple of times we've booked a day-pass at Irikiki Resort. It has gone up in price though.. now AUD$32 (and you get a $12 food and drink credit back to spend at the resort). Get to use their facilities, pools.. wind-surfer, Kayaks etc. Great place. You can book a ride to the island resort for just $5 each (well it was last time) on the water taxi. The water taxi will also detour on the way home to the ship.. via the cheapest duty-free shop in the pacific! 🙂
I did the sport fishing one cruise and the wife did a waterfall. They were average.
https://www.iririki.com/extras/