If you go over to the Holland America board/forum on Cruise Critic dot com you'll find lots of folks who can not only answer your question, but who can also describe them in detail, and offer you suggestions

We've just returned from a HAL cruise with HMC as one of the stops. It is a mosquito ridden island, designed purely to produce income for HAL and there's not much there to do apart from expensive watersports.

HAL warn that the beach has coral under the (imported) sand and you should only walk on the beach with sandals, flip flops etc.

It looks picturesque from the ship but is very boring otherwise. The better stops that we had on Puerto Rico and St Martin were shorter than HMC. They don't want you to spend your money with someone else.

Just to keep this in balance, we were at Half Moon Cay this past March. There were no mosquitoes that time of year - and the weather was excellent.
There were MANY activities to choose from, including snorkeling, watercraft adventure, fishing, glass bottom boat, kayak, biking, hiking, catamaran, horseback riding, parasailing, stingray encounter, nature tour, etc.
We signed up for the nature tour in the morning and one of the snorkeling adventures in the afternoon, and neither of those options were expensive at all.
The beach was full of people playing in the water, the walkways were busy with people going for strolls, people were enjoying their gatherings in their cabanas, others were lounging in the shade of their clamshells, and the free buffet lunch was being devoured by all.
If you mention "Half Moon Cay" on Cruise Critic dot com, you'll find dozens of people who will tell you it was one of the best days of their cruise, and they can hardly wait to go back.