I didn't notice a seafood buffet but we don't eat seafood so it wouldn't have stood out. The regular buffet was better than I expected for breakfast and lunch, but again, I didn't pay attention to any of the seafood options.
Our favorite excursion was whale watching - NCL offers quite a few variations (combined with other things in some cases), all of the boats seemed to follow the same whale sightings so I think any of them would work. Seeing the sled dogs was also really fun - they have an option involving a helicopter and seeing them on a glacier or taking a bus to see them at camp (helicopter version being much more expensive).
The shows were at 7:15 and 9:15pm if that is important to you, in terms of timing coming back from excursions/planning dinner/fitting in shows. I would definitely make reservations for dinner as well, even the main dining rooms filled up with limited availability.
The spa was smaller than expected and in hindsight I wish I didn't book the weekly pass.