The thing I've noticed is that a lot of NCL's negative reviews seem to be written by those with a lot of experience on another line. While this is a natural thing to do it can maybe a little misleading to someone that's never cruised (that line) before.
I agree. NCL is not my favorite line (now that I've discovered HAL and Celebrity), yet I do find their cruises enjoyable. I adjust my expectations for any cruise line, and I hope that comes across in my reviews. You're right that it's hard to do.
The hotel analogy is a good one. And taking it further, there are also differences between hotels of the same ownership. For instance, Springhill Suites and Renaissance are both part of the Marriott brand, but have different feels to them. (And I like them both, again adjusting expectations.) The same can be said about ships within a line.
Many thanks for your great and informative review!