There's a certain know-it-when-you-see-it litmus test when it comes to awesome NBA dunks. It's hard to really explain what makes one great, but Gerald Green 's here is a good example. There's just a certain level of flash that brings out that split-second impulse "OH!" reaction.
The distance Green dunks from here is impressive. But even more so, it's the ease in which he does it. He's so high above the rim that he's literally throwing the ball down into the basket. I feel like he could dunk the ball with his teeth.