Just returned from two weeks in Hawai'i. Overall, was not impressed with some of the "fancy" places like HumoHumo in Weikiki, but found a couple of really great places:
Godmothers in Pahao on the Big Island is OUTSTANDING. New York Italian American place, everything is homemade. Calamari steak was out of this world. I had mine cooked in white wine with capers and very tender. Salad had home-made papaya dressing. Garlic bread was also great and home made. This is one of those classic "hole in the wall" places we all strive to find.
Alan Wong's in Honolulu's is amazing too. Very inventive in both flavors and presentation. Euro-Asian fushion food. Terrific.
Ono Hawaiian on Kapohulu Ave in Honolulu is a great Hawaiian food place. It's around the corner from a Snorkle Bob's and across from the Taco Bell. Try one of the plate lunches on the top of the menu--gives you LauLau (pork or chicken wrapped in greens and steamed) with poi.
There is a fish taco stand just north of the parking lot for Big Beach south of Kehei near Walea on Maui. While the fish tacos are o.k., their smoothies are delicious.