First of all, I've never been to Japan. That being said, I do adore sushi/sashimi (tend to avoid rolls 90% of the time) and probably eat it 3-4 times/month. We did our research prior to our early (7/3 - 7/11) July vacation and decided that we wanted to eat at Koisu twice during our stay, so we made two reservations--and it's a very good thing we did, because we witnessed numerous parties walk in without reservations and get turned away.
All I can say is that this is the best sushi I've ever eaten. I tried the hamachi kama (first time ever) which was a special during our second visit and it was excellent. We ordered a sashimi platter each visit and then supplemented it with numerous sushi/sashimis and were not the least bit disappointed. We didn't have any alcohol on either visit, and the check was between $75-$85 (before tip) each time and worth every penny. This may not be the best sushi place in Maui, or even Kihei, but we did have an opportunity to go to Sushi Paradise and we decided to honor our second reservation and eat here instead and are very glad we did. We sat at the bar both times and were served quickly/efficiently by the chef owner. He was cordial, but not overly-friendly, which was fine with us. We highly recommend this place and will most definitely visit it again next time we're in Maui. I'd give it 6 stars on a 5-point scale if I could.