Just returned from Kauai (and Oahu) so thought I'd report on what/where we ate and make some recommendations.
Our best dinner on Kauai was our first, at Josselin's in Poipu (we stayed on the south side of the island). Though the atmosphere was a bit sterile, the food was interesting and flavorful, the presentations appealing, and the staff enthusiastic and knowledgeable about the menu. We tried the deconstructed ahi sushi, shrimp dumplings with eggplant puree and yogurt (an Asian/Middle Easter mash-up that worked), the kale salad with an oxtail fritter (this was tasty and beautifully presented), and the butterfish. No misses among the dishes.
In contrast, I was very disappointed by Red Salt after reading positive things both here and in the NY TImes. The food, service, and space all fell far short of a fine dining experience, despite its efforts to do so on all fronts. Worst by far was my dish of seven-spice coated ahi with serrano ham, edamame risotto, and a "coconut cloud." I'd asked whether there were any vegetables on the plate and been told there was the edamame in the risotto. There turned out to be a chunk of bok choy that was so hard at the bottom that I couldn't eat that end, and the rest was buried in a heavy coating of thickened coconut milk. The ahi tasted unseasoned and was wrapped in a fairly thick and chewy slice of meat that definitely wasn't serrano ham. It's rare that I spend $36 on an entree, and this one certainly wasn't worth it.
Our other dinners were at Merriman's in Poipu and Bar Acuda in Hanalei. The latter was the better of the two, with decent wine and fairly good but overpriced tapas ($13 for a small dish of beets with a little goat cheese seems excessive even in a tourist area). The food at Merriman's was okay but almost exactly what I'd seen on the menu at its Big Island location six years ago. The place seemed indifferent overall, from the greeting at the door (almost nonexistent, and I overheard someone in another group comment about the person at the check-in desk, "She didn't seem too happy to see us.") to the glasses left on chairs at the empty tables around us. Our server was one positive note, although we were unpleasantly surprised, after asking her about the nightly ice cream and sorbet flavors, to see a $1.25 supplement for one of the flavors--pineapple! This seems petty when added to a $7 charge for two unadorned scoops of sorbet.
Our favorite lunch spot was the Mermaid Cafe in Kapaa, a simple window with a few tables out front. Both the ahi wrap and the tofu satay wrap were tasty, and everyone there seemed happy to be there. Breakfast at the Kalaheo Cafe was also good.
Also enjoyed going to the St. Regis in Princeville for a sunset drink. At least this time of year, the sunset and views are much better than those elsewhere on the island and the staff there make the experience festive.