Koiso was fantastic. The food is incredible and it's not your typical Kehei tourist trap. The sushi was top-notch and the price was reasonable. My wife and I had three sushi rolls and two fresh fish (tuna and salmon) trays and the price was only $34. The sushi was some of the best we've had before. The place is small, but the service is great. They don't attract a big tourist crowd, since we were the only non-Japanese speaking diners, but that should also indicate the authenticity of the food. You won't be disappointed.