Last Saturday, I visited Koo for the 4th time since they opened 6 or so weeks ago.
The food was excellent as well as the service. The chef gave our group some small special non-menu items from the kitchen on the house (grilled mirugai with teriyaki, tiny whole octupus, and tuna, fried-chicken style in a crispy dark brown batter).
I also had the best albacore I have yet tasted since my move here 6 years ago (second best after Nozawa's). I asked for it to be served with garlic sauce and he happily obliged.
Other items were similar to my previous visits (Aji, Tai, Toro, spicy crawfish handroll, tuna tartare with shrimp chips, and jalapeno stuffed with hamachi).
Definitely check out Koo if you are interested in trying a new sushi spot. Waaay better than Ebisu.