After three months of trying a number of restaurant options around Kailua-Kona, we can definitely recommend Splasher's.
The food is consistently good, and excellent value relative to the price environment in Kona. Burgers are the menu special, but the ono (pretty much the only fish on the menu) is also a treat in the fish tacos and seafood wraps.
The location is also hard to beat, especially if you're staying at a hotel or condo in Kona town, since you won't need a car to get here. The restaurant looks over the boat dock, and you'll enjoy a nice breeze off the coast.
Nothing fancy, but not disappointing, which is relatively high praise for Kona cuisine.