Maybe it was me trying to make myself feel better, but the one in the Cayman Islands seemed slightly better than others I've seen. Like someone else said, there is sea water getting in, and fish as well, so it's not a completely fake concrete environment.
The workers seemed to enjoy their jobs and care for the animals and have a good rapport with them. They were playful with the dolphins and the dolphins seemed healthy and happy and playful. One of the ones in another tank was trying to get the attention of the photographer who was trying to take pics of our group.
Speaking of pics, though it doesn't have anything to do with your question, be prepared to be upsold.
We actually booked just the interaction experience and then on the day they offered an upgrade to swimming with the dolphins (I don't remember how much more). That's what we did and it ended up being better because we did the "interaction" first (standing in water up to our waists) and then everyone else left and we got a good 15-20 mins by ourselves.
Side note - I was shocked by how badly the whole interaction went with the rest of our group. There was, I think, 4 families in our group, a family of 5, family of 4 (with 2 toddlers) and a family of 3, plus my son and I. The kids in the family of 5 were HORRENDOUSLY behaved and pouted and threw tantrums (like, teenager age so old enough to not) and wanted to go back to the ship so they could hang out in the teen club. They gave up early. The mom of the family of 3 freaked out when she realized there were fish in the water and refused to get in the water, which then freaked the child out. The toddlers were the best behaved but they were toddlers so got bored eventually, though the parents were impressed they lasted as long as they did. The whole thing was just really strange. But I feel like it made the interaction better for us because the handler just ignored the crazy and talked to us and answered our questions and would bring the dolphin over to show us things and do behaviors that weren't necessarily part of the normal script.