I'll keep this short since there are already 3k reviews, but the whole experience was one I'll never forget.
The crew makes you feel SO comfortable and offers tips for those prone to motion/seasickness. Speaking of which, even if you've never gotten seasick before, take some ginger tablets, dramamine/bonine, sea bands, whatever you need to do. I have a self-proclaimed "iron stomach", never sick in my life, and I had to put my head down for about 10 mins on the ride back to the harbor. My poor husband was definitely hating life, trying not to throw up while sharks were swimming around us, but he pulled through. You're kind of rocking to the waves as you cruise to the site, but once the engine cuts and you slow down, you feel ALL the waves, and they're a good size. So this is my #1 tip: anything and everything you can to prevent seasickness is a good idea.
The sharks were awesome (mostly Galapagos with a couple Sandbars), and the visibility was great. We were broken up into two groups, 6-7 people each, to go out in the cage, usually 2 people "assigned" to a side of the cage, but you can move around freely. You don't get lifevests, but there is an internal bar that runs along the inside of the cage to hold on to, as opposed to the actual cage bars, which was nice.
Our dive was mid-February and the ocean water was surprisingly not freezing! 8am out in the ocean, I was pleasantly surprised. Little chilly, but easy to get in and you adjust very quickly. We swam at our hotel beach later that day and the beach water at the coast was colder than the dive spot. Thought that was so interesting.
Anyhoo, great experience, highly recommended, and will definitely do again next time I'm in Oahu. Thank you for the adventure!