I might be a little biased ;) as i bought a NS 27 last year, but I have found the build quality to be very high. I assume it would be the same for other NSs.
After fitting a new hatch and running cables for various things both of which required grinding into the cabin roof and drilling core holes (in furniture), the laminates and thickness of glass have been impressive. They used very good materials and were (still are) well respected boat builders.
The boat sails well and am sure it would be competitive in races. We recently sailed up the harbour in a 2.3 metre swell and it handled the sea competently for a 27 foot boat.
Guess the cast iron keel would be my only negative, however the keel bolts are sweet after 30 years.