Unfortunately, I have not dined at Hapuna Beach, or Merriman's, however, as you ask in a later part of the thread, did have a horrible experience at the Canoe House.
That said, I agree 100% with the recs. for AW's Hualalai Grille, Pahu i`a and Daniel Thibault's. We did each (DT's for lunch then later for dinner), and I would not do the Kona-side without doing those three again. Each is different, in setting and cuisine, but each was excellent and well worth the $, and even the double drive to DT's.
Of the three that you mentioned, I only ate at Merriman's. I also ate at the Hualalai Grille by Alan Wong at the Four Seasons. Both were incredible, but I'd have to give a slight edge to Alan Wongs. The tasting menu was fantastic.
Try the Big Island Grill for a casual breakfast or lunch. The food is great, portions are big and very affordable.
Here's a breakdown of where I went on the Big Island:
Hualalai Grille by Alan Wong - One of the best meals that I've ever had. It's almost a must to try the tasting menu. His kalua pork - foie gras sandwich is amazing. HRC owned.
Merriman's - Again, another top notch restaurant. Merriman's, like many restaurants, have great relationships with local farmers and it shows in the freshness and taste of their produce. It's a bit of a drive from Kona, but well worth it. HRC owned.
Coast Grille - Very good food with a great view. Make sure and make reservations on the terrace and watch the sunset.
Big Island Grill - Great spot for breakfast. Lot of locals eat here. Seems like everything on the menu is good.
Manago Hotel - Yes, I tried the pork chops. They were very good. Don't let the atmosphere fool you.
Kona Mix Plate - Was once a great spot for local style food, but have come under new ownership and was less than I expected.
O's Bistro - Thought this place was very over rated. The service was bad, portions were small and prices were high. Surprised to find this kind of food from Amy Ota, one of the founders of HRC.
Punalu‘u Bake Shop - One the way to the volcano if you head south from Kona. The malasada's here are great, almost as good as Leonard's in Maui. Tex Drive-In gets all of the press for malasada's, but they were heavy and greasy in my opinon.
Shave ice on this side of the island is pretty dismal. Your best option is Scandanavian, but I would skip it unless you don't plan on going to Hilo.
Not a fine dining options in Hilo. Lot more laid back.
Restaurant Kaikodo - The food was decent, but there aren't too many fine dining options on this side of the island.
Nori's Saimin & Snacks - This place is a must. Their saimin is right up there with Hamura's on Kauai. Tried other dishes as well, and they were all excellent. This place is hard to find but well worth it. 688 Kinoole St
Kuhio Grill - Good place for local style food. Their claim to fame is the 1 pound lau lau. Unfortunately, I haven't been able to find a place that has butterfish in their lau lau the last few times I've been to either Kauai or the Big Island.
Ken's House of Pancakes - Their saimin is also pretty good. They use noodles made from Maebo, so you know it's going to be good. Their pancakes are also pretty good. This place is sort of like Cheesecake Factory, they must have over 200 items on the menu.
Tropical Dreams - Hand crafted ice cream with regional flavors. Not as good as Lappert's but worth a try.
Shave ice - There are two places worth going to for shave ice. One is Wilson's on the Beach, the other is Itsu's. IMO Itsu's is the better option. Itsu's has been compared with Matsumoto's and Waiola. Itsu's is located inside of fishing tackle store, but don't let that fool you. It's a must try.
Good list. The one addition I'd make is Daniel Thiebaut, which is in Waimea, close to the original Merriman's. It's fantastic, sort of a french-ish, asian mix utilizing many local ingredients. Didn't go to the Alan Wong's at the Four Seasons (but have eaten at the Honolulu one, which is spectacular), but we thought DT was definitely superior to Merriman's. The beef brisket was great (not sure if they still offer it) and the fish outstanding. Overall, his flavors work exceptionally well and the freshness of the ingredients is rather apparent. Also, it has a nice rustic, laid-back feel. Cheers!
Pahu'ia was phenomenal! Had a family dinner at the edge of the island. Fantastic quality of food, creative mix and beautiful setting. probably the most enaging sunset in the world. the Canoe House had very good quality food, only the staff seemed inexperienced and young at the time (june 2005.)