What really makes it is the setup. Dodge has the audience laughing with his "damn dirty apes" lines. Then Caesar yells "NO!" Theaters went dead quiet. It's a real CMOA when even the audience is thinking "Oh, Crap!". There's even a reaction shot of Buck the Gorilla with a "what the hell was that?" look on his face.
If you think about it, the first word any ape ever said to a human was a defiant "NO!" How awesome is that?
And then he knocks Dodge out cold with a casual backhand.
Caesar electrocuting and killing Dodge using his shock prod and water hose.
Caesar suddenly appearing on top of that horse. The look on his face as he triumphantly rides forward is priceless.
Especially since, mere moments before, the humans thought they were going to massacre the apes. But Ceasar saw through their plans, sent Maurice and Koba around to ambush the humans, and basically turned the table on their ambush in no time at all. While charging them on a horse he stole from one of the Mounties.
The entire scene with Dodge fighting Caesar in the atrium of the ape shelter. Not only does Caesar take a few jabs from a stun baton and not back down, but he eventually evades the attacks, repeatedly throwing Dodge off balance. He finally stands up for himself and doesn't feel like taking any more Jerk Ass from then on. Then after the Shout-Out to the original with Dodge delivering Charlton Heston's famous line, Caesar stands up tall and straight and roars out an epic Big "NO!". Followed by a slew of Oh, Crap! moments, and possibly, for Dodge, a Bring My Brown Pants moment.
Buck gets one by destroying a police car by ripping up a parking meter and throwing it like a tomahawk. Then a Dying Moment of Awesome by ramming Caesar out of a chopper's line of fire, JUMPING into said helicopter while being shot, and causing the chopper to crash.