We did the Nassau glass-bottom boat and it was just fine. Nothing spectacular, but a good, safe choice for families with younger kids (we had DD9 and DS6) for whom some of the more exciting trips aren't appropriate. We also didn't want to spend a whole lot of time away from the ship and the glass-bottom boat is close.
We made two stops and didn't get to the shipwreck because of "rough seas." I get the feeling there frequently are "rough seas," however, and that sometimes it's code for "the crew doesn't feel like making the extra stop." You also get to see some of Paradise Island, including celebrity homes, which was kind of neat.
We had no problems with fumes, sickness or stairs. I think it's a matter of what your expectations were vs. an objective good or bad rating.