Our experience with the Naupaka Restaurant was enjoyable throughout the whole week we were at Kauai Beach Resort. We ate breakfast every morning with their meal plan (prepurchased vouchers when booking room) and had romantic dinner there one night.
Breakfast Plan - If your hotel room includes a breakfast plan, then this is excellent value for the incremental cost. Otherwise expect to pay $20 each for the hot breakfast.
Good Atmosphere - Dinner was a good experience and very picturesque with the tiki torches, pool view and the water area if you are able to get a water-side table. Service quality was above average.
Food - overall very good for hotel-caliber. Breakfast hot menu items are rotated daily (meats/starches) which offered some variety eating there every morning. For dinner, I had the daily fish and my wife had the Hulu chicken (two huge breasts). Add $4 for salad bar which is recommended and excellent value.
Service speed - during breakfast you may find it a bit slow getting what you want due to the restaurant being busy.
Breakfast buffet - can be a tad pricey without a meal plan
Lack of ambiance - for tables not near the water, ambiance not nearly as nice.