Rachel and I stopped by the Hanauma Bay Nature Preserve when we were on Oahu. Here are the segments we recorded using our GoPro Hero 3 Black Edition.
As far as snorkeling goes, the water was warm and comfortable, the waves were manageable, but the beach / sandy access for this preserve made the water murky at times. We noted that the fish were larger here than other areas in Hawaii. We'd give it a 7 / 10 overall.