Breakdown:
Takeback: Gasquet has a massive takeback on this shot. He uses his left hand to pull his racquet behind him and above his head. This results in a massive shoulder turn. As you can see in this picture his chin is actually over his shoulder and resting on his back. Anyone reading at home should try doing this - its almost as hard as licking your elbow :). It's simple physics - the more energy you store, the more you can release. Gasquet is making sure he is gathering as much power as he can before striking the ball. Why doesn't everyone do this you might ask? Well, a massive take back is time consuming and requires an increased sense of timing. Without perfect timing and early preparation it can be a big weakness of faster courts. Fortunately Gasquet has both, as proven by his success on grass. 
Foundation - Gasquet is leading the shot with his right foot, stepping into the ball. Knees bent, hips relatively perpendicular to the net, and perfectly balanced. He employs a closed stance almost every time, as is customary with a one handed backhand. An open stance one hander is inefficient and frankly illogical (though have seen him do it when he's in a pinch). Unlike an open stance two hander you cannot use your other arm to provide leverage. The ball at this moment is only a couple of feet away from him and yet he is still in full coil.
The swing: Moments before impact, the butt of Gasquet's racquet is pointing at the ball. This is a good habit to form on both the forehand and the backhand. His left hand doesn't release the throat of the racquet until it drops to about hip height. There it stays or sometimes moves back, providing balance similar to a tightrope walker. His right arm is straight at the moment of contact, reducing the chances of mishits and timing errors. Contact is out in front. His head is still locked on the point of impact which is where it stays for much of the follow through. Again, that is another great habit for any stroke, as it keeps prevents you from opening up your foundation during a swing thus adding accuracy and power.
The Flick - This little portion of the swing is what allows for such variety and is what I believe is the key to this great shot. Gasquet's takeback and preparation for every backhand is extremely similar no matter how he plans to hit it. But how he maneuvers his right forearm and wrist at the moments just before and after he strikes the ball is how he can change the trajectory and pace of the ball so drastically. It is hard to describe in words really. And because it is such a quick and violent motion it is hard to understand unless you try it yourself. Fortunately, we can study this portion of his shot by taking a look at the resulting follow through.
The follow through - Just look at this for a moment. It's insane. If you were to superimpose two images of Gasquet's backhand, one during the peak of his takeback and one during the end of his follow through, his racquets would touch. Does your backhand do that? Probably not. And not many pros do it either. Granted his swingpath isn't always as extreme as the one in this picture but it is a good illustration of all the energy he stored up at the start of the swing being fully released. A more conventional Gasquet follow through is shown below. It is important to note that the follow through is a direct result of the flick as discussed above. A flat shot produces a follow through that goes across Gasquet's body and and a racquet that ends up about head level. A heavy topspin shot will feature a follow through similar to the statue of liberty's pose with his racquet high above his head. 
Hope you've enjoyed this analysis!
