Very, very authentic.
You can tell from the menu and the specials that they cater to real asian cuisine and not just the sweet sour port / chow mein / fried rice crowd. The real food here like the salt baked chicken, the spring chicken, the bitter melon. Man this is the place to get real food like as if you were in Chinatown San Francisco.
Great Cantonese food, which means the rest rooms however, are terrible.