well at least they are trying, I would think the credit had more to do with the lack of heat than the wait. If they sent a $75 credit to everyone that had to wait that day, wow!!! Was it a credit toward another cruise or an OBC? I know how you feel and I am not trying to start a war (we have enough of that) but these things do happen, from time to time, not just with NCL. All of us, who have cruised more than a few times can relate stories about embarkation and debarkation that would shock you. Does it happen often? Absolutely no, but it does. The same as missing ports for all sorts of reasons, not common but most of us have experienced this.
YOu keep going back to the cruise line should have held you on the ship: It seems like this was a no win situation for everyone. If they held you on the ship they couldn't start boarding the next group of passengers, ticking those guests off and perhaps even being late leaving NOLA> It seems to me either way, someone was going to be pretty upset. NCL did hold debarkation off for about an hour, but obviously that wasn't enough. You did get a credit at least, if you choose not to use it that is something else.
I do hope, regardless of what cruise line you take next time you have a positive experience. Most cruises are more plus than minus and most that sailed on the Spirit, Nov 30, that I have talked with or seen reviews from had a great time with the exception of debakation.