Summary: Consistently snooty hostesses, great wait staff and phenomenal quality food.
I'll share the bad first since Hiro gets more than ample praise that is mostly deserved. I don't know what it is, but the hostesses at the front of the restaurant have been particularly rude and unwelcoming for the past 3/5 visits. Hiro is very busy and very small with few seats. If you haven't got reservations expect to feel like an enormous burden if you come to eat here. It honestly feels like all the hostesses are 10th grade girls who don't know how to accommodate a party without a reservation. It's as if they haven't dealt with such a perplexing situation before. I wouldn't have let this shortcoming bother me so much if the staff didn't have such poor self control. After seating our party at the bar, one of the hostesses said, "You REALLY should get reservations if you're going to eat here" as she walked away. We live a mile from this place and sometimes decide to eat here in the spur of the moment... It's just poor form and not the kind of attitude that should be present in a quality dining establishment.
Food-wise, I can't speak highly enough of the sashimi. The quality and freshness of the fish is apparent. i haven't explored the sushi scene in cities like LA or SF but would imagine Hiro humbly rivals the quality of the best in these culinary hot spots. Once your seated, the staff seem to all be delightful and professional.