Each restaurant has a 'basic' menu and one or two daily specials. The main dining rooms tend to have more daily specials, the specialty ones less.
I have always found 'Le Bistro' to be the best, Cagney's has been a disappointment on a couple of occasions. I have been on 4 NCL cruises (5th coming up in August to Alaska) and I seem to have about 40 or 50% of my dinners in one or other of the specially restaurants.
I often see complaints about the 'up charges' for the specialty restaurants. The way I look at it I've paid for the equivalent of a meal in a local 'family' restaurant which I would probably pay well under $20 for, the meal I get in the specialty restaurants (and pay an extra $15 or $20 for) is the equivalent of the meal I would get in a high end establishment which would cost me $50, 60 or more - a pretty good deal from my point of view!
Enjoy Alaska....... and the cruise!
I intend to! ;-)