We've been on one. Hated it. Felt like I was stuck in a mall for 4 days. Excursions were nice, but could do without sitting on the boat for hours on end. I think I'm just too hyper to cruise. I like to constantly be on the go. I'm not wired to just relax.
I'm very similar to you. Put me on the beach for five hours where I can walk, run, kayak, and swim, and I am good. Make me sit for more than an hour in a chair on the beach, and I am going crazy wanting to get up and do something. I was in the Dominican with an ex many years ago, and she told me I was miserable to be on vacation with. She wanted to sit on the beach all day and have drinks brought to her by the wait staff. I was able to do that for about 30 minutes before I kept asking if she wanted to jet-ski, paddle board, etc.
I've been on two cruises, both simply due to time constraints making it the easiest available get-away. I think the first one was three nights and the second one was five nights. I will never do another five nighter again. The three nighter was the perfect amount of time for me.
The only time I really spent on the ship was to sleep, get a morning workout, eat breakfast, and then have a late dinner/show. I was off the boat around 9 am each day and didn't get back on until about 6 pm each night. After sex and a shower, we wouldn't be ready for dinner until about 8 pm. Catch a show around 9 pm, and you're ready for bed.
I don't understand the complaints about the boats being too crowded, feeling stuck on it, etc. The majority of your waking hours should be spent off of the boat. The only time you should ever even see many other people is at breakfast or a show.
I enjoyed both cruises and wouldn't be opposed to taking another, but I prefer getting more time to explore a destination. When I think of the highlights of my travels, they tend to be things I found/heard about that were off the beaten path . . . things people don't see/learn/experience about a place just for being there for eight hours during the day. I'd rather have three to four days in one place followed by three to four days in another place rather than a repeated eight hours in each place day after day.
I've never done one, and don't have any desire for one of those types. However, the wife and I have been entertaining doing one of the domestic cruises (on smaller ships), primarily the New England cruise. Those seem to be very pricey though, so still researching it.
I have mentioned these cruises a couple of times on here. While in Grand Cayman, I kept bumping into a family from New Jersey. Dad was very wealthy- CEO of some sort of health/food company, bowling alleys in their house, etc.
His wife kept in touch with another of my exes for a while after the trip, and she insisted that we go on one of the private yacht cruises in the Caribbean. She gave us a link to some of the "companies" that offer these excursions. The crew consists of just two people - usually a husband/wife, best friends, father/son, etc. One is the captain while the other is the chef/server. They cater your trip to what you want. You can pick the number of days, what islands you want to go to, etc. If you want to stay an extra day at an island, no problem. If you want to skip an island and go elsewhere, no problem. If bad weather is hitting one island, it's easy for them to change course and take you elsewhere. If you want to drop anchor and just swim/use the floats all day, no problem. Sunbathe topless? No problem.
I haven't gone on one yet, but I believe they were around $5000 for a week. It's not a bad charge considering your party is the only one on the boat, all of your food is covered, and you get to decide whatever you want to do that day.
That family was skeptical when they went, because they had a high school son and high school daughter at the time. They thought their children would be bored to death, but they ended up loving it.