My wife and I ate dinner at Koishi last night night and it was great. We both had sushi so I cannot comment on how the cooked dishes are but the sushi was excellent. The portion sizes were about average for a sushi restaurant and the prices were pretty good for the quality. The atmosphere is not the greatest but not all that bad either. The good food for a fair price more than made up for a less than stellar atmosphere. If you are near Cotswold this place is definitely worth a try.
Quick tip: Try the Cherry Blossom Roll.