We went to Coral World on past trips, but this was the first trip for the kids, so we went again. It isn't in the same caliber as say the Monterey Bay Aquarium we have here on the West Coast, so in my opinion, it is kind of a grade B sealife park.
If you have something else you might like better, I'd do it.
We also wanted to cram in as much as we could in St Thomas that WASN'T shopping related. My wife and I have been to St. Thomas 5 times now, and after the first 2 times used that as our "sleep in" day because we aren't big shoppers. Couldn't sleep in this time however because of the 6:30 am immigration check.
We did the Skytram in the morning, came back to the ship for a dining room lunch, did the Coral World/City tour excursion, and got a good balance of sights, sea, and shopping.